Caught between two

I apologize in advance for the long story. Alright. So in January of last year (2012) I became involved with a boy we will call A. A and I became very serious very fast and dated for almost 9 months straight, took about a month long break and got back together only to break up again. Our relationship has always been extremely sexually active, if that matters. He is semi-verbally abusive, has borderline personality disorder, and has a very quick temper but I really do love him with all my heart. He's currently refusing to get back together with me because I'm "too dramatic," I "purposefully make him look bad," and he's interested in his friend's cousin. He's told me that we can have a secret relationship until him and his friend's cousin can work out their relationship. I know how twisted this is, but I refuse to leave him. Or refused. I haven't left yet, but lately I've discovered new feeling for my best guy friend, we'll call him B, and have dreamt about him several times. B and I have had sex twice, both times we were both upset about other people having left us(horrible I know), and have both agreed that we find each other extremely attractive but our conversations have never really gone further than that. B's been there for me through all of me and A's relationship problems and I have begun feeling like I might want a relationship with B. Problem is, B likes another girl and I'm not sure he'll reciprocate my feelings either... Should I tell him and risk losing both of them or just stick with being hidden by A?.. Please, any advice at this point will help.