Need advice on what I should do.

So I’ll just flat out and say that I’m the dumbass in this situation. So a few months ago I met this guy and developed a crush on him, but at the time he rejected me. Eventually, he went through a rough break up with his BF and we ended up hooking up, so long story short a few weeks after that and a lot of in between talk if we should date or not, in which we both said some things, I fell in love with someone else I met while abroad. But now I don’t know how to reject him anymore because he rlly clung onto me and I’m genuinely worried about what’s he gonna do if I friend zone him and I rlly didn’t want to make him sad or deepen his psychological issues. I genuinely value him as a person and want to keep him as a close friend, but I rlly don’t wanna date him anymore, I fucked up by not giving up after he rejected me and now I rlly don’t know what to do, so if some of could help me with advice, I’d be rlly thankful.