How Do I Feel Better After This?

I just need some opinions here. My boyfriend and I have been in a serious relationship for over a year and lived together for a year now. He's a wonderful guy and he has made me feel the best and healthiest I've ever felt in a relationship. However, the other night, I was trying to get some pictures off of his phone to use for a scrapbook and found over 900 dirty pictures of his ex. Some of them were of them together. Obviously, I was angry, so I confronted him. He admitted that he still uses them when he pleasures himself because he finds her more attractive than me. He swears he doesn't want to be with anyone else and that he'd never actually sleep with her again. Am I overreacting to be so devastated from finding this out? Is it wrong to expect him to find me the most attractive person because he loves me? How am I ever supposed to feel sexy with him now when I know I'm 2nd place at best?

UPDATE: Thank you for all your support. I guess I was really hoping there was a way to come back from this, but I think you guys are right, it's probably time to move on, painful as that will be.