Born: 06.14.1982, My relationship now was in a difficult situation.

I'm into relationship for over 3 years now and counting. He was born 11.14.1975. Now our relationship faced a difficult situation. I was found out about him and now he need to choose. I don't know what to do. I feel so hurt. I would like to know if we can fix this together? Can we live together in long time or we need to separate for good.