Is it worth the effort?

Ever since I caught my wife in an affair I haven't enjoyed life at all. It hurts so bad to see the woman you love more than anything in the arms of another man locking lips with him. I'm a really sensitive person so her betrayal feels like the end of the world to me. I try to punish her as much as possible now. I let her "accidentally" read an e-mail an ex girlfriend recently sent me. In the e-mail my ex told me my wife was a stupid for ever cheating on me and that if I want she'll make sure I can get even. My ex (who apparently still loves me) offered to sleep with me to "make me feel better and show that (my wife) what it feels like to have your heart stomped on". My wife and I had saved ourselves for marriage and if I was to sleep with my ex I know it would crush her. I love my wife very much despite what she did to me and I wish I could say I wasn't tempted but I am. So tempted that the first time we had since she's been caught I said my ex's name. My wife cried harder that night than she did at her grandpa's funeral and I just smiled. It felt so good to see her in the pain she put me in. We're supposed to start marital counseling next week but I don't know if I should go if I'm tempted to sleep with my ex. My wife says she loves me deeply and wants to save the marriage. She's said even if I went through and slept with my ex her feelings for me would never change. I told her I love her too but I my worst fear of all time came true a month ago and that if I slept with my ex it meant I didn't love her as much as I thought I did. I'm so confused.