I wouldn't say "enemy" per say, but yeah. Do not trust people who remain "friends" with person(s) who want nothing but the worst for you and or your spouse. You can forgive people without allowing them back into your life.
Never thought about how true this is until I left my ex. Everyone's true thoughts about him came out too. So glad I know and completely trust my babe now. Honesty, loyalty, and trust are needed in a relationship.