It's weird, but as a man, I wouldn't mind my wife having sexual relationships with women, as long as I know them and she tells me beforehand. Men, on the other hand? I would never be fine with her having sex with other men.
I just somehow see her having sex with men as disgusting, while sex with women seems pure. I guess reading so much yuri affected me quite a bit...
Cheating, of course, is a betrayal of trust, so even with women I'd still feel bad, though.