I'm disgusted by my own fetish

I have an overwhelming desire to watch my wife have sex with another man. I talked to her about it, and she said she will do it for me. The idea excites me to no end, but I don't want to because it disgusts me. How can I stop wanting it, or should I just give into it and do it? I've been struggling for years with this. It won't go away. By the way, I am in my mid 30s and my wife is in her mid 40s.