Welcome to PC Stillstrong78. Your ex obviously had issues before you divorced i.e. had a mistress, was abusive, not interested in parenting, etc. He has not changed so this is a continuation of who he is. Maybe he spent the time/money on the custody issue because he thought he wanted to be parent but apparently he really doesn't.

You could always revisit the court issue and appeal for sole custody but that involves money (and energy) you may not have. Maybe the best you can do is to be the good, supportive parent you are to your daughter when she is with you and ultimately the ex may drift out of the picture. Kids know the truth without anyone telling them. Your ex's motive? Who knows, maybe he is trying to punish you, but more likely it is his own guilt over the things he knows he did/didn't do.

(((Hugs))) The joint custody thing usually isn't easy. I hope you have a good support system.