Just kidding. See if they can work it out. If it comes to "who you should stay with" (I doubt it will) ask them why they think so. If their answer(s) are beneficial to them, they don't care about you, only themselves.
You gotta keep them separated because if they keep fighting you'll loose both of them just give them space, first ask your boyfriend why he fight with your bestfriend and then ask him why he always fight with your boyfriend. I'm guessing that your bud really likes you and your bf figured that out. dunno ask them.And keep them apart.
It seems obvious that your boyfriend doesn't feel comfortable with the fact that you have a "good guy friend". You and he will have to work that out and come to an agreement. It may come down to which relationship that you value the most, it may not be fair, but few things in life are. Good luck.
Sounds like you may ultimately have to make a decision if they can't seem to get along. I would talk to them both separately, and then think about it deeply... And please don't forget that at your age, boyfriends and girlfriends will come and go, but a true friend will always have your back...;)