help!

so one of my old best friends, I'm not close with her besides a message here and there.. but my bf of almost 2 years found out that her and my ex are related and thinks I been keeping tabs on him.. which never happened. I told my boyfriends mom months ago and asked if I should tell him and she told me as long as I don't see my ex it's okay.. now we aren't doing very good either.. I just Idk what to do