My fiance and I are in a sticky situation with a friend we planned to invite to the wedding. He is dating my FI's ex girlfriend. It was a bad breakup and there have been constant problems and fights with the girl ever since then. My FI told him not to bring her to the wedding as his date, but being she is his girlfriend ettitqutte usually dictates we are supposed to invite significant others even if we don't like them... Is this s special circumstance where it is ok for us to say no?