Sorry in advance for the long post.

My fiancé and I have been together 3 years. I’m 22 and he’s 25. We got pregnant in November. 1 week before my due date I had this gut feeling and finally decided to check his phone. Sure enough I found a muted conversation so I clicked on it and it was back and forth messaging and pictures of some girls boobs and her body in a towel. I instantly felt like I couldn’t breathe how could he do this to me when I’m about to have his child in a couple days I confronted him and kicked him out. I was heartbroken I have never once even messaged another guy since him and I have been together. He went completely Mia for 2 days then texted asking to get his things I said yes and then he finally apologized and said he was disgusted with himself and will never forgive himself. For the sake of my baby I wanted to try and get past it. It’s now almost three months since my son was born and since day one I have been doing it by myself bc we were in the process of buying a house and I have been staying with my parents until the house gets fixed up. My parents don’t like him for hurting me but they’ve swallowed their pride and offered to let him stay here so he will be with me and the baby. Instead of him being grateful he is rude to them bc they told had him they’re disappointed in him. The first week I brought my son home I cried every night into my pillow bc I never pictured doing this alone. I feel so much resentment towards him and he still wants to work things out but anytime I start to feel happy the pictures pop into my head and I feel betrayed all over again. Anytime I feel insecure he gets mad and tells me I need to trust him and if I don’t this won’t work. But all I keep thinking about was how before I found out when I had that feeling I would drop hints like “who are you texting a girl” and even once I asked him straight to his face would you cheat and he literally got mad and made it seem like I was a crazy person for even asking and how dare I ask yet a couple days later I found out he is. I keep thinking if he could come lay in bed next to me everyday while texting another girl everyday how am I ever supposed to trust him. And now on top of that last week I asked him if I could see his phone and he was like "yes I have nothing to hide" so I unlock it and there's a new message from a girl and her convo is one mute and so is my convo! I click the girls text and it was one message saying hey. There was no previous thread and when I get mad he says "its probably one of my old clients you're so insecure its annoying" but why would a random client be muted??

I'm so unhappy but I feel like what it comes down to is I'm so scared to be alone. This was my longest relationship I've ever had and now we have a baby involved. I still love him but I'm so tired of feeling insecure and worrying. I just want to be able to let go without being scared of starting over. My thoughts get the best of me and when I feel fed up I picture him in a relationship with another girl and bringing a girl around my son and it makes me think id rather stay and be unhappy then have someone try and replace me as a mom.