find out why he doesn't want to do something like that. My SO and I have talked about it, but neither of us could do it. It wouldn't feel right for my SO. for me I wouldn't know what to do with 2 people, would my SO think I was simply wanting 'new meat' if I focused on the other person to much? would this make it easier for me to justify cheating? Would the new contact mess with my feelings and emotions? There are a ton of reasons why I would never want to do something like that. but thats just me. find out what bothers him about it, then you will know if a threesome is an idea worth pushing forward. see what I mean?