Alrighty. It seems I was wrong about this being an example of "couple privilege" because I misunderstood where it said the girlfriend wants the husband to choose. I thought where it said that, it meant that the girlfriend doesn't want to be "just friends", that "having" him meant being in a boyfriend-girlfriend type of relationship, with him still married, etc.
That said, I will leave my post up because we can treat this "as if" it's a textbook case. I think it's safe to say that there ARE plenty of cases like this where one member of the original couple IS the one making the other choose. If that be the case, the basic items I outlined still apply.
I apologize for my mistakes. It's a good thing I didn't write all that in the OP's thread.