He cheated

Well I was in a 3yr relationship with a man, that ended horribly. I found out he was cheating on me for the last 4 months of our relationship. To make matters worse we have a 2 yr old son and were engaged to married. I left and he moved in with the other woman they were together for about a year, while I stayed completely single and took the time to truly find myself again. Well he hasn't been with her for about 3months now, he says it was because he wanted his family back..... he calls everyday and I of course can't ignore him because we have a child together. A part of me wants to try and work on it but it's really hard to forgive..... any advice would be greatly appreciated.