Should I leave him?

The fact that I'm even asking this should mean yes. But he said he's going to try very hard to work on himself. Everything was great until a month ago. His son (my step son) has been seeing a therapist, and started crying during a session because he said he feels like he's less loved than his little sister. I pointed out a few things that have been going on around here (favoritism, daughter not listening, staying up all night, etc) and my man complete lost it on me! I had no idea what he had been telling the therapist because I wasn't allowed into the previous 3 sessions. He told me he wasn't holding anything back. Now he says he feels betrayed, and I apologized profusely for it. Basically, we've had sex once in the past month, his attitude has skyrocketed, and I feel like he's only keeping me around as a convenient babysitter since he works nights. How do I handle this? I'm 19, he's 35. It's a huge age difference and I want to handle this with maturity