Most Helpful Guy
Sit him down and meet him. Talk to him calmly, do not get emotional or angry, it's okay to cry though. Ask him why he did what he did, evaluate the conditions involved/his sincerity. Sometimes people make mistakes. I find that closure is the best medicine besides time.
Most Helpful Girl
It's not your fault. If it was not you dating with him, he would do the same thing to other girl. Nothing would change. He found his identity. He is not guilty either. You can not change the reality. He was never into girls. Now he knows it very well. I think only thing he should have done is he should have talked with you before cheating. Cheating is wrong in any circumstances. Now stop blaming your self. You didn't do anything wrong. It is not related with you.