Abusive bf?should i leave him?

Ok so I've been dating this guy for 2 years now. He's cheated on me once early in the relationship. I have yet to get over that and it has put me in a depression since. My bf is loving sometimes and speaks of marriage but when he gets mad at me or in general he calls me degrading names and punches things and threatens my dog to intimidate me. But he's really sweet and loving other times. Makes me feel alive. I done want to question our relationship but I've talked to him abt it and things haven't changed. What should I do? I'm 17 and he's 19. Please only mature/ adult responces.