How to get past it?

I've been with my boyfriend for almost 5 years, things used to be perfect when we were younger, we had more time to spend together, we could do whatever we wanted to do, whenever we wanted to do it. Now we both work, I have to study, and we have a 6 month old boy. Recently things haven't been so great, I guess the biggest thing is that a couple weeks ago I got a message from a woman asking "is this your boyfriend?" With a screenshot of their conversation attached. He added her, asked her if she was the one who worked at the burger king in our town. (He got us food there the night before), she asked why then said yes. She wasn't trying to keep the conversation going at all. But he kept trying and then he sent the text "I don't mean to overstep, but you're gorgeous" and I just started to cry. I looked at her profile, I noticed that she's really pretty. Since I had the baby I've been really struggling with how I look, I weigh the same as before I became pregnant, but my stomach is filled with stretch marks and it's a lot more flabby than it has ever been, on top of that I'm breastfeeding which I love but my boobs look so different, it's bad. I always tried to hide myself from him after that but he always told me he thought I was beautiful no matter what. I believed he meant it. Anyways, after I read the text I packed my clothes and the babys things we left to my moms and I tried so hard not to text him (he was at work) but I lost it and sent a message. He told me over and over it was "just a compliment" "It's not like I cheated" I know maybe it's not as big as actually physically cheating, but it really broke my heart. He told me how sorry he was and a week or so later I was back at the house. We've fought since then, it hasn't been the same and I keep looking at her profile and just comparing myself to her. I can't stop, I'm depressed and everything he does, I question. He told me that he wouldn't have told me about it. I look at her and then I look at myself and think why would he even want me? Honestly. I'm sitting here with the baby while he's at work, I just looked at her picture again and I'm so sad. I agreed to come back and try to work on things, I thought I could get over it easily since he didnt really "cheat". I feel depressed. My trust for him is completely gone. But I agreed to come back and work on things, how do you get over something like this? Because being here, depressed, wondering what he's doing when he's out. Is obviously not healthy for me or the baby. I want to be over it so bad. If you read this far, thank you❤ I have nobody to talk to here. Any advice is so appreciated.