He wasn't popular. He knew it. Hell, everyone knew it. Sort of a… reverse popularity. He didn't know how he'd come to be friends with James. From there, he'd just… become one of the Marauders. He should've been happy, he supposed.
Still, he never quite felt like he belonged. Sirius and James were always together, causing trouble more often than not. Remus was always there to make sure they didn't go too far - and if they did, he had a certain amount of authority to bail them out, being a Prefect and all that.
Peter, though… he never could really do anything for them. He never felt as if he was any help, and so he wasn't happy. And it wasn't like being part of the group had really made him popular. He was just that guy that hung out with the popular kids.
So no, he wasn't happy. He was far from it; until she started hanging out with them. She was absolutely beautiful. He could never help staring at her. When they sat out by the lake, he would admire her hair in the sunlight, redder than he would've thought possible. He loved her eyes - deep, emerald eyes, the kindest, most beautiful eyes he had ever seen. Even her name was beautiful; he had always liked lilies.
He was so in love with her, and even better: she was actually nice to him. Of course, Remus was always nice, and James and Sirius were almost never truly mean to him. But Lily… she would talk to him, ask him how he'd been. She actually cared about him.
That's why it hurt so much more than it should've when she started dating James. Why? She'd hated him before she started hanging out with the Marauders. She barely tolerated him when she did join the group. So why did she have to go and break his heart like that?
It might not have even been that bad, if it wasn't for the fact that she had chosen James! Of all people, why that pompous, arrogant James? He always got everything he wanted - people loved him, he rarely got in trouble for his mischief, he was talented, good looking - everything that Peter wasn't.
So that's why he was doing this. He was still in love with Lily; he always had been. He just couldn't stand the thought of her with him. They even had a kid! That asshole was trying to inflict a second generation of Potter on the world.
That couldn't happen; then it would just be his school days all over again. The little Potter boy would be popular, and talented, and loved by everyone. And of course, being all that, he wouldn't ever stop to think about the other people in his life - the ones who admired him, and despised him at the same time.
I'm sorry, Lily. I've always loved you. Steeling himself for what he was about to do, Peter Pettigrew allowed himself to be guided to the chamber of the Dark Lord.
"Lord Voldemort? I know where they are."