I recently went through a broke up and she cheated on me 6 times. This is what helped me:
I looked at this kid, and by no means am I talking myself up or anything, but damn she downgraded. The kids face was hideous, his breath smelled, he had disgusting scabs on his face like a meth user. Right then and there I knew it was time to move on. Being I am still in college, I took full advantage of all of the horny drunk girls and just after 1 girl I knew it would be easy to get over my ex and wanted to get more but from other girls. Trust me I was in the same boat. During my break up, all of my friends would say "there are plenty of fish in the sea". But I couldn't see that and its obvious you can't either, but thats expected. You have to take my word for this, and another bro here on EF can vouch for this. There ARE in fact other girls out there who are better in many ways. You will find them.
For this one time you have to think of all the bad things. What made you unhappy? Write them down.. If there was EVER a moment where you started doubting your relationship or felt like you just wanted to be away from her, then thats the only assurance you need that it wasn't meant to be. Don't think of the happy things, I'm sorry to be a blunt ass but you probably won't get her back so the happy things are just memories now.
Start talking to a new girl. Don't alway go for looks brotha, I've learned that lesson a lot. Get a girl with brains, who is loyal, not shady, doesn't have only guy friends. This will help you because regardless if you say you aren't, every guy gets jealous. Talk to this girl for a month or so, get really comfortable around her if you can tell she is doing the same. This always helps me.
Good luck, hope this helps at least the slightest bit.