I need quick help, I'm devastated :(?

My boyfriend of 2 years has suddenly changed. Up until around two weeks ago, he treated me like a princess, cuddled and kissed me in public and we only ever had small arguments, never really big fights. But suddenly, he started just being off with me, he broke it off last week, saying it was "too hard to be with me", and then asked if he could come back the next day. I forgave him, and thought it was just a minor wobble. Since then, he has been speaking to me sporadically, saying he loves me and that he is sorry and wants to be with me forever, but other times ignoring me, or deliberately saying things to hurt me, like commenting on other girls and also bringing up how he's asking another girl to his house each month to complete their art folios together (this girl has had a known crush on him for quite some time). When I've questioned this behaviour he shouts and says he's done nothing wrong, and turns his phone off when I become upset. I really love him but I know he's treating me horribly, I don't know if there is someone else or whether I've done something to upset him because he won't speak to me. I really need advice because I'm sick of being constantly upset and in tears :( xx