How can I get my mom to ease up?

I'm 18 years old and I'm a full time college student at a university that's 4 hours away from home. I love my parents and, in my opinion, I've always had a good relationship with them. My dad seems to have no problem accepting that I've grown up. However, my mom seems to believe that I should be around her constantly. She gets angry every time I leave to go spend time with my boyfriend (whom I've been with for 19 months) or my friends. I'll admit, I was a bit of a homebody until I was about 16. I went to friends' houses on the weekends and that was about it. But then I got a job, a car, and a boyfriend pretty much all at the same time. Ever since, my mom guilt trips me all the time about how she never sees me (even though she does). She cries when I leave the house and acts like I don't love her. She tells me I don't call her enough, but I don't really call anyone very much, not even my boyfriend. I just don't like talking on the phone much. Every time I go to my boyfriend's house or go with one of my friends, she slides in some comment about me not loving her. It really makes me angry. I don't like being accused of not loving my mother, because I do. It happens all the time, and we'll get in an argument over it every once in a while. So she'll say something like, "We used to have such a good relationship but now we always fight." No we don't. She expects us to never argue, which is impossible and when we do, she seems to forget about all the time I DO spend with her and how well we DO get along. I just want my mom to accept that the older I get,the less dependent I'll be on her, but she never listens to me. :/