How do I control my emotions around my guy friend?

I have been home since monday from the hospital. Well Tuesday I decided to go to the gym with my mom. I was sitting in the area near the basketball courts reading when I noticed an old schoolmate named Alen. I haven’t seen Alen in nearly three years. Well Alen came up to me and was just like “did you go to ‘d’ middle school?” After I told him I did, he was like “yeah, I remember you!” We were talking for a long time. Alen and I were never that great of friends in middle, but we didn’t hate each other. We just never had classes together because of different grades and because he was a “popular” in middle we never talked. Anyway, my mom was watching us from a far and said Alen was grinning from ear to ear, seemed kind of nervous to talk to me and was checking me up and down. I like Alen, but there are a lot of problems going on right now that I don’t want to put him through. I’ll state all of them. First, I have been undergoing chemo and don’t want him to have to even know or see anything like that. Second, my friend whom I cared a lot about passed away back in Jan. I never want to date because of that. I cried last night because I can’t get him out of my head. Thrid, Alen is only 15 and I’m 17. He looks like he is 17 though. Alen is a sweet kid, but I don’t want to hurt him. I know two people can never care for one other without it being doomed. I mean one of the two will eventually hurt the other. Whether it be abuse, leaving them, or even death, One hurt the other. So, how do I make it seem like I don’t care for Alen. Do I become mean or what?