What should i do about him?

I just started dating this guy and before me and him started dating he got out of this relationship with this other girl that broke up with him for no reason. Well when we started dating it was all good i mean he talked about his ex a lot but I understood because he got hurt by her. Well yesterday he was texting me saying im going to go to the movies well I couldn't go to the movies and I already new that his ex was going to the movies to. Later that night his ex started texting me saying i'm with your bf i'll tell him u said hey. Well I tryed to kill her with kindness saying oh thanks have fun with him. and then he texted me saying that they were going to this basketball game instead. Well sure enough his ex went to. He was still texting me and then his ex texted me saying i love how ur texting ur bf while im with him. I got so mad and I didn't talk to him for the rest of the night. Well he said he would nvr cheat on me and I said okay. Well just now he called me and said hey u wanna listen to this song so i said sure and it was about someone doing someone else wrong. at the end of the song i asked who showed him the song and he told me his ex showed it to him. He talkes about her all the time when we promised each other that we wouldnt talk about our ex's! What should I do?