I need outside opinions

I need insight from someone else other than the little voice in my head. I left my baby father and parter of 8 yrs. recently we had an argument about him not being ready to commit after so long and a baby. I found out he’s been lying about communicating with the other mother of his child behind my back. I always knew they were talking obviously I can’t stop that but this time he went as far as deleting conversations, changing her contact name to a guys name and putting the convo on DND so it wouldn’t pop up when using the phone. When confronted about it he told me it’s because I’m crazy. This isn’t the 1st time this person has brought problema into our relationship and frankly I’m not fighting over a man. He’s insistent that it was just conversations about his son but if so, why hide it? My gut tells me leave because this whole shit is shady. Am I overreacting or what?

I want to add we’ve been having relationship problems for a year now after having a baby, I’ve really tried to put my half into reviving our relationship only to find out he’s been doing this behind my back.