So let's say your spouse's best friend used to have it out for you. They tried to make you seem like a bad person and tried to get your spouse to leave you, going as far as setting them up on a blind date. They refuse to be your spouse's friend because your spouse won't leave you. Years go by and the old friend wants to reconnect with your spouse. The spouse sees no reason for you to be upset about it.

The "bestfriend" turned your spouse's family against you in the beginning. The "bestfriend" also wanted to date you before this relationship but you never entertained it. Your spouse told the "bestfriend" about your bedroom activities knowing they used to like you, and everything went downhill from there.