Finding out that my husband was going to leave me

I knew my husband was cheating on me but I didn't know that he was actually going to leave. This happened 12 years ago but recently I was speaking with my mom "n" law and somehow our conversation lead to the time my hubby/her stepson was cheating on me. I guess she knew that I knew it all but I didn't. I didn't know that his whole family was involved in his decision to stay with me. It hurt so bad to know that he was just going to up and leave. Now my problem is do I say something to him about how hurt I am or do I move on? I am trying to not give him an attitude about some old history that we worked out. I don't want to destroy the joy we have now.