1. An unfaithful spouse keeps an ex-lover as a friend.
Infidelity is an enormous hurdle for a marriage to overcome, but just ending the affair is not enough, says Kaye. For a marriage to fully get past adultery, the unfaithful half of the couple cannot maintain a "friendship" with the former lover. No matter what he or she says about the innocence of such a relationship, "nothing good can come out of it," notes Kaye.