Need advice :/

My boyfriend and I recently had our first baby together, a few days ago I found out he’s been talking to his ex.. I don’t know how long they’ve been talking but she knew I was pregnant & that we live together. In some of their convo she brought up a sneaky link like a damn teenager & he brought up a date on Friday which is tomorrow.. I only found out bc an instagram link got sent to my phone & he asked for the code & I clicked it thinking it was our shared account & he got locked out.. When I clicked it their messages popped up.

He apologized & was super sincere about it & showed he felt like shit. I just feel super insecure about the situation now & need to know what he can do to build my trust back. We’ve been together for a very long time & have been solid the whole relationship.. I just don’t know how I can trust him after it. I still feel a way about it & can barely kiss or look at him.. I suggested therapy because we do plan on working on things but we are single now & will work on it.