Please Give me advice for my girlfriend trouble?

I don't know how to approach this problem of mine. I've been with my girlfriend for about 8 1/2 months, and I still can't seem to relax around her SOMETIMES. It is very strange. Most of the time, I don't know how to make conversation with her. I feel socially inept and insecure. I have basically no friends and I'm very introveted, so I don't have much of a life outside of my full time job and college courses. The thing about my gf is that a couple of weeks ago she said she loved me, and I could tell she meant it. She has a four year old daughter. I notice that my gf is more introverted and laughs less around me than others. I sometimes think that I bring her down. I also think that she is settling sometimes. You see, she has cerebral palsy, and I do things to help her out. I sometimes think that she might love me for the things I do rather than for me. She doesn't take advantage of me, and she is very independent. I just don't know what to make of our relationship. Advice, please?