It seems as though you were both contempt with the relationship rather than being truly happy, and I think that's totally fine, it's nice to have someone there for you regardless. I personally would have never stayed with someone who had cheat on me, but then again, there are a lot of people who would have made it work, so I suppose it comes down to personal choice, I'm sure you had your reasons for staying.
I've been on this board for a few years, and I see plenty of threads like this, people who are sad seek sad and depressing wallpapers, they listen to sad music and stuff like that which is the opposite of what you should be doing. You need to focus on making yourself happy, however you can. Do all of the things that make you happy, let go a bit.
I have been thinking about my emotions a lot since I broke up with my girlfriend. She was the first person I really opened up to, and I learned a lot about myself, what made me happy and what made me sad. This made it a lot easier to talk to friends and family about more personal things that I never thought I would. It may sound cleche, but talking to friends and family always helps, they're always there to support you, everyones been in these situations.
I've come to think of happiness as a bell curve of emotion. It's easy to stick to one side or the other, it's the transition thats the hard part. Once you've got a more positive outlook on things, and your in that positive mind set, these things wont get to you as much. You'll soon realise that you really are better off either without her, or with someone better. Every break up is another opportunity to get things right next time. You'd be better off with 9 failed marriages and 1 perfect one at the end rather that being stuck in your first for the rest of your life thinking about what could have been.
Just do what makes you happy, it's as simple as that, I know you can do it.