Broken relationship

I had my son about 6 months ago and im a ftm. My sons father and I have been broken up for over a year.(i found out i was pregnant after we broke up) we were together for a 1yr and half prior. But we've known each other for almost 13yrs. For the sake of our son we have been living together for the last year. He pays rent I pay everything else. I cook clean do our laundry grocery shop pay internet utilities etc. I've been wanting to try to rebuild our relationship and I thought for the majority of my pregnancy that's what's we were doing. However recently I found out that he been seeing a mother girl while I'm at home with his son all day. I think it's time for me to leave the apartment. My sons father wants me to stay even though he stays out all night and is seeing someone. I'm just lost on what to do