I'm not going to be overly judgemental, but I see that you still have feelings for him and that's why I'm posting.
A man who is capable of deceiving his wife for 2 years, isn't trustworthy. I don't believe that he was guilty, because it lasted 2 years and only ended when you knew he wasn't leaving his wife.
How could you trust him in a relationship?
This is a man who had at least one affair and possibly more. When you look at the qualities you want in a man do honesty, and trustworthy or integrity feature on your list?
If they are not important to you, then go ahead and reply to him.
If you are truly ashamed of what you did, you wouldn't think about replying and would want the affair to stay in the past.
I think your past relationship with him will taint any future relationship, because of how started back then.
I'm going to to send you a link via PM that I think you'll find useful.