Help!

Okay so my husband has this female friend. Back in HS my husband would cheat on his ex with this so called friend. When he and I started dating I felt very uncomfortable with how much he would text her. When I told him he would say they were just good friends. After hs he and I took a short break. I found out later that on this break they would have sex. Here we are now years later and she texts him everyday and he texts back. She wants to hang out with him but only if I'm not there. Am I crazy for being so angry about this????