I don't really see why you should support that. In your case your wife is not closeted and living a lie, everything is out in the open. So deciding to change you for someone else, regardless of sex, is no different than if I decided to change my wife for another woman. We give stuff up to make a commitment to someone else. It doesn't always work out and I'm not saying people should stay together when they don't want to, but I am questioning your pre-acceptance of your partner wanting to shag someone else even though that would clearly make you very unhappy.
"Prefer women" could be in a sexual context, romantic context, platonic, etc. and the commenter above didn't define it. I imagine it's hard enough for bisexual people to be asked if they're "living a lie" by having to choose a side.
They aren't choosing a side, they're choosing a person. Being bisexual surely just opens the field to more potential mates, but once you're with someone the same rules apply as to folks in any other relationship. And I don't want to sound too conservative - if you choose to be with someone and both agree to have an open relationship of some kind, or any other mutually agreed kind of thing, that's no-ones business but yourselves.
In this case though, they're saying their partner is pansexual - open to many kinds of sexual activities. And they're saying that they'd be accepting if their partner needed to go and do sexy stuff with someone else even though it'd cause them a lot of pain (that's my reading of it, not having a platonic friendship with someone else as you mentioned). I'm asking why? Having a different to hetrosexual appetite before going into a relationship shouldn't give you special rules once you're in one - it's absolutely no different than if a hetrosexual person wanted to sleep around. OK if your relationship allows for that, really not OK if it's going to cause your partner/spouse/love pain, as they said.
