You are responsible in making your life hell. Think about this. Initially she told you that she had an affair with someone. She may not told you about physical relationship. But later on she herself told you, this is her honesty.
Suppose you marry another women who may also have physical relationship with someone but she does not disclose with you then? Everybody has past. She may not mature enough at that time so this mistake happened by her. How much punishment you will give to her?
Please don’t live in past. Live in present. 2 years is too much time. You have already taken peace of your and her life. So now be a mature man.
Breaking a relationship is not easy. This will also not give you gurantee that in future you will get a good women.
Start looking to her good thing.
Do some meditation.
If you feel then go for psycho therapy definately.
Please let me know your thoughts on this.