Cheating 😡😩

So my boyfriend of nearly two years went to magaluf in August and told me he didn't do anything... Stupidly I believed him I mean why it's shagaluf... Until this girl text him one morning saying "Morning babe 😘" he was out the room so I went on his phone 🙈 and read the whole conversation between them.. "Meet me here.. Meet me there... Thanks for last night.. I'll come and see you once I'm home.. You've made my holiday" obviously I was absolutely distraught as I was pregnant at the time with our little boy who is now 10 weeks old. But in those messages I noticed a picture of them two kissing so I set it as his home screen, locked his phone and acted like nothing was up. He came back into the room gave me a kiss and went back out with his phone after a few minuets he comes bursting through the door with the most shocked, worried and surprised look in his face. I couldn't look at him, eventually after he calmed me down we spoke, I felt like I needed to break up with him but I physically couldn't 😩 any way now 3 months down the line after the whole stupid mistake he did we are stil together but I can't seem to get it out my mind that he has slept with another girl! I do love him and I'm trying my hardest to forget but I don't know how.. Please someone help me... What do I do? 😓