I absolutely cannot stand my best friend's guy?

My best friend dated a guy for over 4 years, who was near perfect, but they decided to amicably part ways. Since then, she has been seeing this new guy who can't seem to keep a job, isn't very good looking, and is beyond possessive. His salesman-type personality is extremely brainwashing and although she's normally an very independent girl, she's now taking the blame for things between them that aren't her fault solely because he turns everything around on her. He's very jealous and insecure and it's driving me nuts. My best friend is a model, in college, makes great money, and has everything going for her. She could have any guy she wants, but she keeps getting roped in with this loser. I've vented my frustration numerous times and she knows how I feel about him, so I flat out told her I can't stand him and I will not be fake and pretend to like him because it is not who I am. She's asking that I at least be nice, but I just can't find it in myself to do it. On top of it all, he's a recovering drug addict with a bad temper so I'm truly just worried about the situation she's getting herself into. Trying to be nice to him just because he's with her makes me feel like I'm saying I'm okay with him, but I'm not. Am I overreacting on this? Any other girls who have had similar situations with their close friends? I'm trying to be patient and hope she sees the light soon, but in the mean time, I could care less if the guy gets hit by a bus.