I would kill my husband if I found out that he was having an affair. I think I have even threatened cutting off his balls if I ever found out he was having one.
I am even dead against him having a fmf with me. I came close to trying one with him and a close friend of mine some 15 years ago now. It got as far as skinny-dipping with her and him but then nothing more eventuated and I don't know if I was relieved or disappointed. Part of me was certainly curious to see it, but a huge part was worried he'd enjoy it too much.
So this is where there double standards are. See I love the idea of having another guy join us and being free to have sex with both hubby and the other guy. I have no issues at all with it and don't expect my husband to either. And I don't know if that is really a bad thing or not. I mean I still want him there as a part of it but don't see adding another guy as a threat, wheras I see another woman as a threat.