Don't Bet On It by spikescrypt
I do not own Teen Wolf.
Derek isn't fighting with an eight year old kid over Stiles, except he sort of is.
Once a week Derek and Stiles have Scott and Allison's son Jason stay overnight in their apartment so that his parents could have some adult time to themselves.
Or as Stiles has taken to calling it, "Wolfy Wolfy Smoochy Boom Boom Time."
This wouldn't be a problem except that Derek was convinced Jason was trying to steal Stiles from him.
The kid was constantly following Stiles around, making goo-goo eyes at him and laughing at all of Stiles' jokes like they were the funniest thing in the whole entire universe.
Stiles along with Scott and Allison seemed to think this was "just precious" and told Derek he was being ridiculous.
Derek knew better though, he saw the way Jason constantly sniffed Stiles neck when being put to sleep.
The kid was scenting what was his.
If this was all the evidence that Derek had demonstrating Jason's crush on Stiles then Derek probably would have tried to ignore it.
Except there was also the way that Jason treated Derek.
The kid would stick his tongue out at Derek for just walking into the room.
He wouldn't even eat anything that Derek made; vowing only to eat what was touched by Stiles.
Stiles would brush it off and claim that Jason just had a strong attachment to him.
Derek knew better.
This was why he was keeping a very close eye on Scott and Allison's little demon child while he was over that night.
As soon as Jason was dropped off he immediately hugged Stiles and asked to play Alpha Wolf.
"Sure buddy," Stiles said.
Alpha Wolf was a game where everyone takes a turn pretending to be an alpha and all of the other "wolves" have to mimic whatever the alpha says or does.
"You can be the alpha and Derek and I will be your betas," Stiles told the boy, ignoring Derek's look of outrage.
"No! I only want to play with you, not Derek, " Jason screeched.
"That's not nice Jason; you have to let everyone play," Stiles scolded.
After three minutes of Jason chanting "Derek can't play" Stiles was finally able to persuade Jason to let Derek join the game.
Much to Derek's disappointment.
"Grrr," growled Alpha Jason.
"Grrr," growled Beta Derek and Beta Stiles.
"Derek is a poopy head," says Alpha Jason.
"And that's the end of Alpha Wolf," says Stiles.
By dinnertime Derek seriously wanted to throw the little brat off the roof.
He constantly had to chant to himself, "eight years old, he's eight years old" over and over again.
At dinner Derek showed off by slicing a piece of meatloaf with one long sharp claw.
"Daddy has spikier claws than you," Jason told Derek. "His claws are just like Wolverine's."
Derek refrained from asking the boy if he wanted to find out just how sharp Derek's claws really were.
When Derek declared it was bedtime Jason gave him a swift kick to the knees.
Stiles had to physically restrain him from strangling the devil child.
After they had finally put Jason to bed Derek and Stiles decided to watch some television in the living room.
Not five minutes into Game of Thrones and they heard a loud thump upstairs.
"I've got it," Derek said, removing his arm from around Stiles' shoulders.
"Try not to eat him," Stiles teased.
Upstairs Derek found Jason manically jumping on the bed.
"You're supposed to be asleep Jason."
"I'm not tired Derek the Booger."
Derek growled threateningly at the eight year old.
"When I grow up I'm going to marry Stiles," the boy announced.
"Don't bet on it," Derek said.
Ten minutes later Derek joined Stiles back downstairs and proposed.
A shocked and thrilled Stiles accepted.
In the morning Stiles told Jason the good news and was rewarded with a tantrum.
"No! No! No! I told Derek I was going to marry you. Me not Doodoo Face."
Stiles glared angrily at Derek. "Please tell me that you didn't ask me to marry you just because you were competing with a child."
Derek looked guilty and sheepish as he nervously moved toward Stiles.
"That's not the only reason," he said.
"Not the only-," Stiles sputtered. "It shouldn't even be one reason Derek!"
"I know that believe me I do. It's just that last night he said he was going to marry you and I realized that I didn't want anyone even an aggravating child for God's sake to even consider spending one day with you. That if a freaking eight year old can see how incredible you are then it was only a matter of time before others do too. I realized that I wanted to be the one who got to call you my husband and wake up to you every day knowing that you were mine."
Derek took a long shaky breathe and hoped Stiles wouldn't kick him out of the apartment.
"You are such a moron," Stiles said, which made Derek's heart drop.
"I can't believe you seriously think that anyone could ever steal me away from you. Cause let me tell you something Derek; no one could ever make me not want you. I've wanted you since I was a teenager and I always will."
Derek pulled Stiles firmly against his chest. "So will you still marry me?"
"Yeah I will," Stiles answered grinning.
An angry Jason kicked Derek in the crotch.