Cheating Boyfriend feels Guilty!

I just really need some opinions on my situation, I'm not sure what to do but my kids father has been having an affair with a married woman from his job since July 2018.

His reason being that I was brushing him off constantly whenever he'd try have sex with me. At this time, I was heavily pregnant with our son who is now 4 months. On top of that, we have a 1 year old who I am constantly running after and picking up and cleaning up after etc, with a 7lb baby in me. I'm a small person, I'm 5"0 120 pounds and I gained 50 pounds with my son. Anyways, I was exhausted.

We have split up a couple of times due to me thinking he was entertaining someone else but he always said he isnt doing anything just hanging out with his friends, either way he was never home so I didnt know for sure what he was doing but he would never come home and help me so I threw him out 2 or 3 times just breaking up and making up. We moved into a new place, he says he'll be more available to me and that he is sorry for putting me through this, it's been week 1 and he has been keeping his word so far.

BUT, yesterday, I get a call from the husband of the woman that my boyfriend has been sleeping with.

He left his phone in her car YESTERDAY, he told me he was stepping outside to smoke and when he came back his phone was missing but I didnt think anything of it. Happens to be, he met up with this woman to break off their relationship because he wants to be with me. I obviously did not know he was sleeping with a coworker, and I know we patched things up and I know he was breaking up with her. But I feel shitty and I dont know what to do. He broke down in front of me apologizing and telling me he wants me and his family, it was just he was "horny".

What would you do in my situation?