I do not own Big Time Rush, no matter how much I want Kendall to be mine! Or Logan... Or James... Or Carlos... :P Anyways, here's the story!

It didn't make any sense. Sure he was protective of her, he was pretty much her brother, but that still didn't explain it. The feeling he felt whenever he saw her. Kendall's little sister.

When it was her sixteenth birthday, she wore a bright red dress that clung tightly to her curves and no matter how hard he tried, he couldn't stop staring at her. She looked amazing, breathtaking even. The way the sunlight bounced off her wavy brown hair, her radiant smile, her perfect skin. She glanced over at him and winked. His heart fluttered in his chest. What was wrong with him? It didn't make any sense.

When she got her first boyfriend and brought him home, James couldn't explain it. The strong feelings he felt. The hatred, envy and the other feeling he felt in the pit of his stomach. Something that made him incredibly uncomfortable with the whole situation. He pulled Katie aside after dinner, wanting so desperately to talk to her, "Katie…"
"What?" Katie replied, annoyance lacing her voice.
"You know Harry Parks is a player right?"
"Psh," she chuckled, "please James, stop making me laugh! He's the sweetest boy I know! Besides, you told me to go and find a nice boy."
"Yeah," James replied appalled, "When you are like 40!"
"Really… You sound like my brother."
"Maybe that's because I'm practically your older brother!"
"No you're not James! Besides, would an older brother be jealous of his younger sister's date?"
He hadn't thought of that. Jealous? Of Katie's date? Could that be the reason as to why…? NO!
"Jealous? Are you insane Katie? You're like 12."
"I'm 18 actually and technically, I can date whoever I want. So, STOP telling me what I can and can't do!" She then grabbed his tie and pulled him closer so their faces were millimeters apart. "Got it James Diamond?"
The scent of her hair became overwhelming, blocking out all common sense and her breath sent chills up and down his spine, making him shiver slightly. He gulped loudly, and not because he was scared. "Understood." He just managed to get out through the fog engulfing his brain.
"Good." She nodded and let go of his tie. "I see that we've come to some kind of understanding." And with that, she left.
Jealousy. It, for some odd reason, made sense. The other feeling he felt in the pit of his stomach. The feeling that made him want to puke when she saw her laughing at her boyfriend's jokes. The feeling that made him want to punch the guys living lights out. Maybe, just maybe he was jealous of Katie's new boyfriend. But why? She was Kendall's little sister. She may as well have been his little sister.

When Kendall and Jo got married, James couldn't have been happier. He, Carlos and Logan were the Best Men and Katie and Camille were the Bridesmaids. Katie had worn a maroon backless dress which accentuated her figure perfectly. James couldn't describe her beauty that day and began to wonder how radiant she would look in a white dress and she walked down the aisle, a long train following her as she walked towards where he was….
"JAMES!" James snapped out of his daydream to see Kendall smirking at him.
"Hey man!"
"Daydreaming I see..."
"Yeah sorry man. I was a great wedding though!"
They were at the reception, and from what James could see, his friends were already in the thick of it. Carlos was already busting his moves on the dance floor, being the 'King of the Party' as he liked to call it; Logan was clearly enjoying his make out session with Camille, who finally after ages of waiting had finally become his fiancé, and Kendall of course was with Jo, who were both stooping over him with something obviously on their minds.
"So," Kendall began, looking briefly at his wife with a small smile on his face, "Have you had a dance yet?"
"Not yet," James replied yawning in the process, "It's been a long and tiring day." Kendall stared at his friend, his eyebrow raised. "Ok, maybe later then." James finally agreed.
"You know," Kendall said, as he sat next to him on a chair, fixing up his tie as he continued, "You should dance with Katie."
"You know! Katie. You should dance with her."
"Why? Doesn't she have her boyfriend to dance with?" James replied, his voice laced with jealousy.
"No. He broke up with her."
"What?" He replied shocked, staring at his friend.
"Yeah, he broke up with her yesterday. She said she should have listened to you. That you were right."
James considered for a couple of moments. "I don't know... Maybe not."
"Dude, I know you like her. It's been obvious for ages."
'You like her… You like her…' Kendall's words kept repeating themselves in his brain, 'You like her.'
Suddenly everything made sense. All the feeling he had felt towards her for the last few years.
"Yeah, OK you got me. I'll dance with Katie." He got out of his seat and started to walk towards her, a small smile played on his lips as he thought about his recent epiphany.

James Diamond was in love with Katie Knight. And everything seemed to make sense.