Unsure

So my boyfriend and I are fighting more lately and I feel like he's always siding with other people rather than me. Our roommate is a jerk and is always yelling at me or threating and making ultimatums. My boyfriend doesn't have my back at all through it. He won't stick up for me at all. The mere fact that he let's him speak to me the way he does is upsets me. I really have thought he was the one since we've met. He's my best friend and I want to marry him, but he's being so mean and acting like he doesn't care. Part of me wants to leave but I don't want to be alone and I give everyone the benefit of the doubt.. I'm so scared he's not it for me. Lately the thought has crossed my mind... I just don't know what to do right now.