Needing advice

Me and this guy have been talking since July and hanging out since August. We’ve slept together and also I stay over there most weekend but he still hasn’t define the relationship. Well, a couple days ago I saw on his phone he is still using dating apps and talking to other girls on them. He told me straight up he doesn’t play games with girls and when he’s talking to a girl it’s only her. Well obviously he lied and idk how to approach the subject