I(19F) don't want to be friends again with this guy(19M) after I rejected him, maybe it might sound a bit crappy at first but I really need to get a second perspective on the matter.

When we were in 3rd year of highschool I became friends with this guy (let's call him Derek) because we shared common interests and it was fun to hang out. In the last year of highschool, when we were going home, he confessed to me that he liked me and asked me if I wanted to be his girlfriend, I internally panicked, not knowing what to say or do because I really liked him as a friend but didn't like him in that way. Didn't want to say yes because it would be pretty unfair and didn't want to say no because I was afraid of loosing a close friend. I told him I needed time to think and we went our separate ways, he sent me a text the next day, telling me that he was sorry for suddenly dumping such information out of nowhere(probably noticed my discomfort) and told me that it was okey if I didn't have the same feelings and that we could keep being friends if I wanted to. I felt relieved at that information and said that I wanted to keep being friends. When we went back to school, for some days he was pretty distant, I honestly didn't blame him and understood he might have needed some time first, so I kept it too, then we progressed at being friends again and hang out.

The next year(aka last year) both of us being in different universities, we kept hanging out as friends and all. In one of those hang outs when we were going back to each our home, he told me that he needed to talk to me and if I had just a moment, I told him yes even tho I felt so much nerves, it was late at night, I was worried that I got late to my house(I still live with my parents and needed to get on a bus to get home) and more worried at the fact I could feel that twist in my stomach of how we were going to talk about those feelings and the relationship again, I could feel how it was coming when we walked to a park near the train station. He told me that he didn't stop liking me, that he tried to stop, tried going out and meeting/dating other people but he just couldn't, he told me that I could accept his feelings and date if I wanted to or we could stop being friends because he felt like he was torturing himself by being around me. I understood it completely, I once had feelings for a guy that I had to move schools from just so I could go on with my life. I told him that it was okey and that I get it.

When I got home I felt bad because I lost one of the only two friends I kept contact with from highschool(the other friend it's a girl which I go to university with now. I've told about this whole situation to this girl too even reminding it to her recently a few months ago because she forgot). Derek and I didn't talk, hang out nor text anymore, and honestly after some time I was moving on from it and doing pretty well.

A few weeks ago, I went to this girl's birthday party(She invited friends of her from highschool), what I didn't know is that Derek would be there too, I was uncomfortable the whole time he was there, tried to ignore his presence the whole time and my nerves calmed down when I noticed he left.

(In all honesty I didn't know why this girl didn't tell me she invited him considering she knew about the situation, didn't ask her about it either. But she was going trough some things too at the time with the break up she had with her boyfriend and being friends with him again immediately after it because of a promise they made when they started dating or something like that)

The thing is that, a few days ago he texted me again(when I was at another birthday party by the way) since it was in the middle of a party I decided to not answer immediately; his messages said that he had time to think for all these months to figure out his feelings and figured out he wasn't really in love with me, that it was only friendly love and asked me if we could start again from cero. I decided to not respond immediately because I was in a birthday party and thought that I could just tell him that we could when I got home the next day since it was a sleepover. I was completely wrong, I haven't responded to him since then because I feel so bad just thinking about it, I feel my stomach twist and a weight all around, at first I though I wanted to be friends again, but now I'm not sure at all if I really want to. Just thinking of him makes me feel terribly sick, not sure why.

I really need some advice on what I should do or at least some opinions about the situation... Thanks for reading through all this wall of text and hearing me out...