What do I do? Do I leave or work it out?

I’ve posted a while ago about how my boyfriend was messaging another girl and she was flirting and he kept entertaining the conversation all that but wasn’t flirting just kept carrying it on and when she asked for a pic of him he send a shirtless one and when she asked him if she looked cute he said “I mean you decent” I’m not even sure what that means. Well anyways I didn’t know really if it was cheating so I just told him to not text her then he told me he quit smoking bc I told him it made me sick and just he was doing it was to much where if he didn’t he would freak out and leave places too so I told him if he didn’t I would take a step back well he was showering I had to pee so bad so I asked to come in he’s like yep and I walked in there’s some sitting on the counter I said wtf is this n he had his mouth opened and smiled probably because he was nervous. But I was mad since I asked how he was doing with it all that making sure he was okay and he lied:/ so which hurt me. In the beginning of the relationship he was doing actual drugs and promised me he wouldn’t no more n did it behind my back so. Now all I think about is that, I feel sad half the time:/ I feel like I’m being lied to most the time. What do I do. We have a baby on the way which is why I’ve stayed.