Living with people is the worst?

Long story short, My brother has helped me get a job and all after the big move from OK. I've been doing great except for the fact that I've been living wih him for about a month now with his girlfriend and her 2 kids, and another coming in 2 months. The problem is that my brother's girlfriend picks fights with me constanatly. NO matter what I do she talks down to me like I'm a retard and tells me if I don't like it I should just leave. My brother pays all of the rent yet she wears the pants in the relationship, obviously. I have done nothing to either of them, especially her, to deserve this kind of treatment. I don't think I should be getting harred like this EVERY single day, especially when I'm paying rent. I just got this job and it is perfect but I can't take her mouth any more and I don't know what to do. I got to the point where I'm going crazy and might go into the military. I need advice quick. Am I the wrong one here?