I feel physically sick, how do I move on from this?

Whenever someone is attracted to me and openly expresses it, I begin to feel physically sick; as though I am going to vomit. I have been talking to a boy in the year above me at school recently, just out of common interest in our conversations and friendship, but he has begun to show an interest in me that is beyond that. He started asking me to go out with him in his car at lunchtime, and I agreed to do so, but not because I am attracted to him. I felt strange about the situation because I do not like it when someone who I am not physically attracted to shows an interest in me. I have not encouraged any interest on his behalf, so I have not lured him into a false belief that I am available for a relationship with him. I have not been at school this week because I suffer from depression and I could not cope, but yesterday, a friend told me that every day he has continuously been asking where I am and looking for me in areas around the school. She has said that he is acting like a stalker almost. Then I got a text message from him, because he has obviously attained my phone number from a friend who should not have divulged this information. Now I feel physically sick and slightly afraid, like I want to escape and never see him again. It is not that I have anything against him, I just don't know how to deal with this situation and I don't want a relationship. Now everyone is asking my friends if I am going to be his girlfriend, which is really frustrating because I haven't done anything at all to suggest that this is a possibility; it is just him who likes me. I don't like the idea that he has been looking for me constantly and acting with stalker mannerisms. I have to go back to school on Monday and I really don't want to see him, but I know that I cannot avoid him forever. Why do I feel like I am going to vomit every time I think about him, and how can I move on from this? I really don't want a relationship. Thank you.