Flirty or innocent… Thoughts…

I never go through my husbands phone because I trust him. My last marriage ended after 13 years and I did not have that same trust with him. I would always go through his phone because he was always friending and liking other females on social media that he didn’t know. Anyways, I was on my husbands phone calling my aunt because mine was dead and decided to scroll just one more scroll on his messenger to see if there were any females there and sure enough, there was one. Someone my husband used to work with at his current company. I wasn’t really going through his phone but more curious and had saw she said that she missed their banter conversations. He says he never felt like he was being flirty and his definition of banter was different than how I think it means. He sent her a picture of our son because she has 5 kids and would talk about kids. Am I over reacting? I think banter is flirting, teasing, etc. not causal. He won’t let me read their messages because he doesn’t want me to break that boundary and trust him. He deleted Facebook and messenger because he said it would help me trust him if he didn’t have those anymore…. We’ve been together for 4 years. This man takes care of myself, 3 kids from my previous marriage and our son. He paid for a house when I was leaving my ex and he didn’t even live in it until we got married after having our son. He’s a good guy, but coming from my last relationship, it’s hard to trust on something like this.