Help should I stay or leave him alone baby almost here

So me and my boyfriend have been on and off this whole pregnancy because he would rather go hang out with friends and get high. Well a few weeks ago he kept going to a friends house were there his friends sister was there and I just didn’t feel right about something so I told him to stop he didn’t want to do I told him I was done if he wanted to hang around a females who had sex with all his friends that went over there then he could stay over there we’ll come to find out he has sex with her to be said he was drunk and he thought he lost me and it just happened what do I do he said it was a one time thing but how do I know when he stays there