Happy V-Day to you. I hate the OW did that too you but good for you in not responding!
My thoughts on infidelity are this...You can either deal with him cheating in the hopes to get him back, or it is a deal breaker. If it isn't a deal breaker, then let him do his thing for now. If you two get back together, let him know that won't EVER be accepted/put up with again. The hardest thing in the world is to let something like this happen WHILE knowing about it. You are a strong woman with really good friends. You can handle this and we are here for you. Everything you want to say to him or her, come here and say it to us.
When he leaves, go GAL like crazy. Enjoy every minute you can. Celebrate you and who you are becoming. Do something you never did but always wanted to.