Rejecting someone nicely?

So I sit next to one of my really good friend’s twin brother in most of my lessons and we get on really well, but she recently told me that he told her he has feelings for me. This made me feel a bit awkward for him but I didn’t want to embarrass him by saying anything so I just let it be.

However he’s started asking me to meet up outside of class quite often and ,although i genuinely would like to spend more time with him, I am not at all romantically interested in him.

Basically my question is what should I do? I don’t want to lead him on in anyway and I’m worried that I might get his hopes up if I just go along with everything, but I also don’t want to embarrass him by clarifying that I just want to be friends (which would make him aware that I know about his feelings), especially since he hasn’t actually made any advances on me yet.

advice?