Someone over on AO3 requested this and I figured I'd post it here too. Enjoy the angst :)

Derek felt the slight irritation tinged with panic well up in him again, "Stiles, you are not coming with us." He repeated. "We certainly don't need your help spying on the alphas and even if we did I wouldn't let you come."

"Why?" Stiles challenged. "Because I'm human?"

Growling, Derek spat out, "Because you are a human with no training as a hunter, no special powers and no fighting skills. You would only get yourself killed if we get caught."

Stiles was silent for a moment before asking, "Since when do you care if I get killed?"

Derek looked stunned. His entire body reacted to Stiles' words as if he had been punched. The irritation that had welled up in him so quickly was gone in an instant as he took in the teen staring him down defiantly. When he finally spoke again his voice was unsure and quiet, "Stiles, do you really believe that?"

With half of a nod, Stiles answered, "Well I did. But now when you respond like that I'm not so sure."

Derek sighed and dragged his hand through his hair in frustration. "Of course I would care if you got killed. Why would I not care?"

"Maybe the constant threats? The wall shoving? The always acting like I'm just an annoying accessory to Scott?"

Derek looked guiltily back at Stiles. "Yeah. I guess I can see that sending the wrong message." Conflict darted across his face and he made a decision then that he had been debating for years. "Stiles, I kept pushing you away because I didn't want you to get hurt. I've been trying to protect you."

Stiles looked doubtful. "From the very beginning? Why?"

Taking a deep a steadying breath Derek replied, "Because you are my mate. I thought if I pushed you away you would be less likely to get hurt."

Thick silence hung between them at Derek's words and he started regretting his confession almost immediately. Of course Stiles would react badly, why would he want to be Derek's mate? It had been stupid to tell him. Derek was just scared that if he didn't finally tell the boy the truth the idiot teen would keep following them into danger without thinking.

Derek was about to turn around and slink away when he suddenly noticed that Stiles had moved closer to him while he was distracted by thoughts. In fact Stiles was so close Derek could feel each breath that came from him flicker across his own lips. Stiles looked him straight in the eye, making certain he was paying attention, then he snaked a hand behind Derek's neck and dragged him in for a kiss.

He was only shocked for a brief moment before instinct took over and he was kissing Stiles back with all the pent up passion he had felt since the day he realized Stiles was his mate. His hands tangled into Stiles' hair as he angled his head better. Derek darted his tongue against Stiles' lips and elicited a soft gasp from the boy which Derek took as permission to press further and he felt Stiles' mouth open further to encourage him.

When they broke apart, Stiles was gasping for air and Derek was breathing fine but looking completely disheveled. "Why…" Stiles panted, "the hell… did you wait two freaking years to tell me?"

Derek's face turned more serious as he answered, "I didn't want you to feel obligated to be with me."

"Sorry to burst your self-hating bubble, Derek, but I've wanted to be with you for at least a year and a half."

Derek pulled Stiles in for a brief and much more chaste kiss then wrapped his arms around the teen and took a moment to just enjoy the feel of having his mate in his arms. "Stiles, please tell me you'll stay away from the alphas now? Do you have any idea what I go through every time you follow us and put yourself in danger? I can't concentrate when you're there."

"Yeah, I guess. I get what you're saying. I don't like it, because I want to be there and help the pack, but I understand. I know that having your mate in danger, especially when he's just a weak human, is probably the most distracting thing that could happen in a fight."

"You're not weak, Stiles." Derek answered forcefully. "You're strong in a completely different way than me. It's just that your kind of strength does nothing to help on a battle field. Your kind of strength is meant for holding the pack together and being the brilliant mind behind our plans."

Stiles nodded a bit with a small grin on his face. "You should get going." He finally stated. "Weren't you supposed to meet Scott five minutes ago?"

Realizing Stiles was right, Derek made to leave. He had only taken a few steps away from Stiles when he stopped. Derek turned back to the teen and closed the distance between them once more. He lowered his mouth to press against Stiles' once more and as he pulled away he whispered, "I love you."

Stiles' grin was so large that it seemed in danger of splitting his face in two and he whispered back, I love you too. Be safe, Derek."

Derek nodded and headed to meet Scott. As he ran, he marveled at the warmth filling his chest. He had known Stiles' was his mate since the day they met but he hadn't realized how good it would feel to have those feelings returned. He felt whole. The gentle smile on his face refused to go away and in his mind he could finally actually see a happy ending for himself.

He saw Stiles waiting to welcome him home, he pictured a wedding and one day some kids, he thought of the whole pack coming over to their house to visit. All of the things he had told himself he could never have were actually possible now. Derek would never have admitted it for fear of losing his dark brooding persona but he felt like he was floating.

Scott noticed instantly that something was up. After a brief inhale a smile broke across his face and he said, "Finally. Isaac and I were wondering when you two would get around to realizing you were crazy for each other."

Derek was too happy to be annoyed that his feelings had apparently been obvious to his pack. Together he and Scott headed off to keep an eye on the alpha pack. The pack had been up to something lately and Derek wanted to see if he could figure out what it was.

They arrived at the warehouse the alphas had been hanging out at lately and crept closer. Derek leaped up to the second story window ledge and peered in. Scott stayed below and kept an eye out for movement. Derek saw Deucalion talking to the twins; yelling at them actually. He strained to hear what Deucalion was saying.

"You've lost control of her completely! Ennis' death was supposed to focus her not make her into a wild card."

It was then Derek noticed that Kali was not with her pack. That was also the moment he registered Scott yelling his name and the alpha pack turning to look straight at him. He pulled away from the window and dropped back to the ground in time to see Kali knock Scott off his feet. She was raising her claws, preparing to strike at the vulnerable Scott, when Derek tackled her from behind with his own claws already out. The two rolled together in a mad rage of claws and teeth. Derek felt his strikes landing more often than not but he also could feel the rip and tear of his own flesh as Kali gave as good as she got. Scott was trying to find an opening to rejoin the fight but couldn't see any opportunity. Deucalion and the twins had come out of the warehouse by then and Ethan was screaming to Kali, "We need him alive, Kali. Stop!"

With a sickening sound, Kali's claws quite suddenly dug into Derek's chest and burst out the other side. He let out a roar of agony. Kali smiled as she ripped her hand back out and answered Ethan with, "Ennis' murderer has no place in my pack. I want him dead."

That was when Scott noticed the distinct smell of wolfsbane burning his nose. He looked back and forth between Derek and Kali and realized with horror that in her claws she held a hollow bullet. A bullet that Scott was positive had moments before been filled with wolfsbane. Wolfsbane that was now festering in the gaping hole in Derek's chest.

Derek was writhing and gasping on the ground at Kali's feet. His claws clutched at his chest as he tried to tear the wolfsbane powder out. Black lines streaked outward from his chest in ugly patterns and they inched closer to his heart with each minute that passed.

Scott roared and burst into action. He ran straight for Derek ignoring Kali still standing beside him. Kali seemed confident in her success so she made no move to stop Scott as he heaved Derek up and practically carried his alpha to the Camaro. Derek cried out again in pain as Scott lowered him into the passenger's seat but he didn't fight. As Scott broke every speeding law in the book to get to Deaton's he also dialed Stiles' number.

"Stiles. It's Scott. Get to Deaton's."

"What?" Stiles' voice was tinged with panic. "Scott what happened? Is Derek okay?" As if in answer, Derek let out a gasp of pain when Scott hit a slight bump in the road. "Was that Derek?" Stiles was bordering on hysterical now. "Scott, tell me that wasn't Derek."

"He's going to be fine. Just get to Deaton's." Scott hung up then and concentrated on avoiding any other road bumps. He glanced over at Derek a few times and his worry grew with each glance.

They pulled into Deaton's and Scott dragged Derek out of the car as quickly as he could. Derek's eyes flashed red as he bit back another roar of pain. Deaton stared wide eyed for only a second before he opened the mountain ash barrier to let them through.

"Wolfsbane." Scott explained. "Can we get it out in time?"

Deaton took in the damage and the proximity of the poison to Derek's heart. Deaton slowly shook his head. It was enough for Scott to understand that his alpha was going to die.

An anxiety filled voice called out from the lobby. "Scott? Are you here?"

"Back here, Stiles."

Stiles tore into the room and stopped dead when he saw Derek. His eyes widened and Scott could already see tears forming. Stiles was at Derek's side instantly, grabbing his hand in his own and demanding that he stay alive. Stiles' hands shook as he clung to Derek. As Stiles raked his eyes across the damage Scott saw the mental connections happening in his best friend's mind. "This is wolfsbane isn't it?" Stiles whispered. Derek chose that moment to cough up a large amount of black blood and Stiles shuddered. "It is. This is exactly what happened when he got shot before." A bit of hope entered his face as he looked at Scott. We saved him last time. We just need wolfsbane."

Deaton spoke up then. "Stiles, I don't have any wolfsbane here."

"So go get some!" Stiles yelled.

"Even if I knew where to get any, Derek doesn't have enough time left for me to get it to him."

Stiles' expression fell and he clutched at Derek's hand even harder. "He can't die though." He whispered. "Not now."

Derek groaned again as the white hot pain pumping through his body intensified. He felt like every cell was on fire. He could vaguely make out Stiles' voice somewhere in the distance but all it did was remind him of how happy he had been earlier that day. This wasn't how it was supposed to end. He finally had found a reason for hope in his life and started to believe that he would be happy. This short agonizing death had not been included in his plans. The images of marrying Stiles and raising pups together faded out as another spasm of pain racked his body. He could feel the creeping tendrils of wolfsbane nearly touching his heart now.

"Damn it, Derek!" Stiles screamed. "You can't do this to me!"

Scott flinched at the pain evident in Stiles' voice and he quietly backed out of the room followed quickly by Deaton. This was not a moment for them to intrude on.

In a quieter and much more broken voice Stiles repeated, "You can't do this to me. Derek, I need you…I love you. Just an hour ago you were telling me that I was your mate. You can't just tell me something like that and then leave me." Stiles was sobbing so hard now that he could hardly get the words out. "Please… Derek… I can't lose you." Stiles felt his breathing start to fail as he gasped for air and black spots danced across his vision.

The desperation in his mate's voice pulled at Derek's mind and he wanted nothing more than to comfort Stiles and ease his worries. The stuttering breaths coming from Stiles were enough to bring Derek back to the present. He fought the pull of the welcoming unconsciousness and squeezed Stiles' hand gently. Stiles was staring at him with panicked eyes and Derek wheezed out, "Breathe Stiles." Stiles nodded mutely but still failed to pull in enough air to feed his starving lungs. More forcefully this times Derek commanded, "Stiles, I need you to breathe. Don't you dare die with me. You need to keep breathing… keep living." Derek wanted to keep talking but another wave of pain crashed down on him and he found himself struggling to even stay awake. His eyes connected again with Stiles and he was glad to see the boy actively concentrating on getting his breathing under control. He was looking down at their entwined hands and the slow deliberate breaths in and out reassured Derek that Stiles was not going to give up.

Derek's whole body gave a jerk and then lay still upon Deaton's table. Stiles looked up at Derek, fearful of what he would see, and felt a part of him die as is gaze met the snaking black now entwined across Derek's heart. His chest no longer rose and fell.

It took Scott and Deaton over an hour to convince Stiles to let go of Derek's cold hand. Even then, Stiles just retreated to the corner of the room and sank to the floor. His arms wrapped around his legs and he gazed unseeingly into the distance forcing himself to breathe. Not because he wanted to, but for Derek. Stiles would keep breathing because it was the last thing Derek had ever asked of him.