Boyfriend Trouble..HELP! Really ASAP!?

So my b/f has a addiction to and he gets on my case saying I am watching it...well today I was waiting for a friend to call on his phone and I was just looking at his pictures and somehow I ended up on something else on his phone and they were naked women after he swore on his dad he wasn't looking at it. Well I brought it to his attention in a nice manner and his first reaction was to hit me across the face and then again and I kep asking him why he was doing this to me and he started screaming at me to get out of the room and he pulled me by my hair and grabbed me by my neck and threw me out and he also told me he didn't deserve it. Why does he treat me this way? Did he get angry because I found this stuff on his phone? I honestly don't know why? I am only a eighteen and he is like in hes older tweenty's. I have no family and I really like this person but this is not right...I just don't know what to do. Please help.