I think he's stalking me...what do I do?

Sorry if this is long. I used to have a crush on this guy way back when and of course it faded. Turns out he liked me and when he asked me out, I said no because I liked someone else. Then my little crush sort of came back and he found out. Unfortunately, he has a girlfriend now so she found out as well. That's when my feelings for him faded away. However, I remember one time I needed a ride to school because I ran out of gas and really had to turn in an important paper. I called everyone and no one could do it but him. On the ride over, he was driving like a psycho, really jerky, and then told me to never tell his girlfriend that he was giving me a ride. I agreed. Just a few days ago we were texting and I asked him why we never hang out like we used to. He then said, "I don't think (girlfriend's name) would like it," and I said, "What, does she not trust me or something", and he said, "Yeah". He then went onto say, "We can't hang out but we can have fun". Me being naive, I had no idea what he meant by that and even asked what he meant. He asked, "Didn't you want to get with me", and I was shocked. So then I cut off communicating with him and went to school. Well I only have one cl in the evening and that's on Wednesday evening. As I was leaving, I drove in the parking lot and something told me to stay in that aisle though I really wanted to go home. That's right when I saw his girlfriend's car. Of course I recognized it because I remembered what make and model it was, as well as her distinctive license play design, and the ornaments she has hanging from the mirror. Now his girlfriend never went to the same college I go to and already has two degrees. I remember once she told me and my best friend that she's never going back to school. I know that she also lets her boyfriend borrow her car a lot and he goes wherever he wants to go. I also feel like a rotten friend because I never told my best friend this and here I am, had a little crush on her brother, and now I don't know what her brother's intentions are, not do I want to know. Now I think he's following me. Help...please?