Look, as a shelia, its no different from a bloke. She is now happy with datng uber-Mormon boyfriend and I am happily dating other people as well. That would only encourage her to give up other standards that really are serious and to become like the typical Western degenerate.
And of course, when it happens, no one the leaver or the faithful spouse could have predicted it.
Anyway, before you marry you should work out anything hypothetical that might come up in the future.