My boyfriends best friend is annoying as heck. 10 points?

Me and my boyfriend just started dating a couple weeks ago, and my boyfriends best friend matt decides to declare about twice a day that he doesn't like that we're together, stuff like "I don't LIKE it!", "Why are you guys holding hands? It looks awkward", and he is always calling me a 'beetch' (sorry about the beetch typos, I can't spell it on here), behind my back even though no one agrees with him because I really don't even talk to his friends. My boyfriend even asked matt why he thinks I'm a beetch, and matt seriously couldn't think of anything. Last night I said "Matt, I have something to say. For the past couple weeks you have been acting like a 5 year old. I tried to ignore it, but seriously cut it out. I'm sorry that you think I'm a beetch, but you need to grow up and keep your feelings to yourself, have a nice day", he replied saying 'ur a dummy', to which I said 'well that was really mature..' We are all 16 and 17.What should I do?!