Possible to be truly comfortable with non-exclusive

It's an ongoing discussion with my best friend. Without personal history or background right now, he says that no woman ever actually wants a relationship where her guy is seeing other women. He says that even if a woman says she expects, understands, accepts or even encourages the man she is dating to date other women inside she resents it.

I've definitely seen women who said they were okay with dating other people but clearly had problems with it if it actually happened But I've also known women whom I believe were perfectly happy to be in an FWB type relationship where there was no expectation of commitment or exclusivity, just an agreement to be prudent and use appropriate protection if hooking up with other people. Am I mistaken and they said those things only because they felt that an open relationship was better than no relationship?

Your friend is wrong when he says "no women ever". Of course there will be women to whom this rule doesn't apply.

But as a general rule, I agree that women tend to be uncomfortable when they are in open relationships.