Troubling Fantasy

Hello there, this is my first time writing about the things that keep going on in my mind. I'm a happily married man. I've been married for ten years, but for two years now, I have been thinking about watching my wife in bed with another man. I don't know if it is okay, but when I'm thinking about it, it really makes me so turned on. It never crossed my mind to tell my wife about it because I think she will freak out, or maybe she will let it happen. I really don't know what to do. I hope you guys can help me or give some advice on what I should do. Thanks a lot.

— Antonio, 30