Ex’s coming back

So me and my ex broke up 4 months ago and since he has a new girl. But honestly I still love him. I’ve tried to move on but my mind just goes back to him. We talk a lot and I we talk in school but today he went to my car just so we could make out. I tried to resist but I couldn’t. As much as I don’t like his new girl I don’t wanna do this to her. What should I do about this?