Lincoln had only met his alternate universe self three times, but three times had been enough to know that he couldn't stand the guy. He was brash, arrogant, cocky, confident, and a strong leader. In short, he was everything Lincoln wasn't, and that annoyed him.
Peter, on the other hand, seemed to have no problem with the guy.
It started with a case they worked on together a few months back. Him and Peter had been forced to spend a whole week living in the other side while they pursued a genetical engineer from their universe who had escaped through the bridge to the other side. They'd traveled all of New England in a Fringe Division van with the other Lincoln, and while this was the definition of a nightmare for Lincoln, Peter appeared to be having the time of his life. He joked with the other Lincoln, they teased each other, talked tactics, and the differences in pop culture between their worlds. Lincoln was starting to feel like a third wheel by the end of the trip, and was all too glad to find their quarry holed up in an abandoned motel on the edge of an amber zone in Upstate New York.
That could've been the end of it, and Lincoln wouldn't have had to deal with his doppelgänger for months, except Peter really had struck up a good friendship with him. Every week since that case, he would travel to the other universe to have drinks with the other Lincoln, and every now and then the other Lincoln would come over to their universe instead.
Lincoln took pride in the fact that he wasn't the jealous type, had never been in his life, but every time Peter would mention the other Lincoln he would feel this pang in his chest that left him in a sour mood long after Peter had left.
"Sounds like you're jealous," Astrid told him, glancing at him over the file in her hands, barely allowing him to finish his story before responding. They were in Walter's lab, well into the late night hours, pouring over their most recent case files while Peter enjoyed another evening with the other Lincoln. Lincoln thought this would be a nice escape from his thoughts, but somehow he'd ended up pouring his heart out to the only person who'd listen instead; Astrid.
"I'm not the jealous type," Lincoln said patiently, though he was starting to annoy himself every time he said that because he knew it was no longer true.
"You've noticed Peter gets along really well with the other Lincoln and feel that he's going to fall for him because they have more in common than you do with him," Astrid said, a little weary, "Lincoln, that's normal."
"Is it? Because I've never dealt with anything like this in my life," Lincoln muttered, feeling slightly annoyed, "I mean, he'd still be attracted to me, but not me at the same time, you know?"
"Just talk to him," Astrid said, "Peter may be reserved about his feelings a lot of the time, but if you ask him something directly he would tell you the honest truth."
Lincoln considered this for a moment, wondering why he hadn't come to this conclusion on his own already.
When he arrived home that night, Lincoln found Peter at the kitchen table, crossing things out on a piece of paper. When he saw Lincoln, his face lit up, and Lincoln couldn't help but smile himself.
"Where have you been?" Peter asked, putting his paper down.
"At the lab with Astrid," Lincoln said, walking over and kissing him, "missed you."
"Missed you too," Peter said, picking up his paper again. Taking a seat next to him, Lincoln saw it was a list of bands and singers.
"What's the list for?"
"Lincoln, uh, the other Lincoln, asked me to recommend him bands from this side to listen to. I'm making him a mix CD."
And just like that, Lincoln was back to feeling sour.
Peter noticed too, because he put his list down and furrowed his brow, concerned.
"Alright, what's wrong?"
"You've been spending an awful lot of time with him, that's all," Lincoln said, frowning at the list, "you're even making him mix CD's now."
Peter looked dumbstruck for a second, then chuckled. Lincoln glared at him.
"What's so funny about this?" He asked, feeling all that repressed jealousy finally boiling up inside of him.
"Come on, Linc..."
"So you're just going to deny it, then?" Lincoln asked angrily, "You're going to deny that you don't like him? That you feel like you have more in common with him than with me? Because from what I've noticed over the last month, you've been getting real chummy with him. You're going out with him every week!"
"And yet here I am, spending every day and night with you," Peter said, still grinning despite Lincoln's constant glaring, "why are you worried about me spending time with him?"
"Because he's me, but better," Lincoln said, too angry to feel pathetic at this point, "he's bold and heroic, he's witty, he's sarcastic, you get along great with him, and you'd probably make a perfect, heroic couple together!"
"Lincoln," Peter leaned across the table and lifted Lincoln's chin with his hand, "he's not you."
"He could've been me," Lincoln grumbled, shoving Peter's hand away.
"But he's not," Peter said, smiling warmly, "we may have a lot in common, and yeah, I get along great with him, but there's nothing there past friendship."
Lincoln frowned, attempting, and failing, to form a counterargument.
"You're not like him," Peter went on, "You're not rash, or cocky, or overly confident like him. You think before you act. You're quiet, a little shy at first. You're reserved. You're adorable, and you look great in glasses," he took Lincoln's hand in his and kissed it lightly, "no other Lincoln could ever replace you in my eyes."
Any anger or jealousy Lincoln had felt up until then immediately dissolved, leaving him with a warm and fuzzy and much more pleasant feeling instead. He pulled Peter closer and kissed him deeply, wanting to erase any doubt in Peter's mind that he felt the same way about him.
"I'm sorry," he mumbled, pulling away slightly and looking Peter straight in the eyes, "I've never been the jealous type."
"You don't have to apologize for anything," Peter said earnestly, then grinned and folded up his list, "now, stop being silly and come to bed with me. I'm exhausted."