I think it just depends on his situation as far as relationships. If he's a semi-shy type and hasn't had a girlfriend in a long time or ever I've seen this happen here and there. My roommate's friend he grew up with nextdoor won't even call, won't talk to him, and it not to be taken personally either - he won't even spend time with his own dad.
I'm guessing though you know what qualities caused you to click as friends, if you don't know for sure just think about it, I'm sure you'll figure it out and I'm sure you'll figure out how to find those qualities in other people. Once you do that you'll probably sooner or later meet someone who'll bring you into their group of friends and once you have about 3 or 4 your good - even if you aren't a clingy person it still helps to be busy but at the same time be there to help em with a move, when a car breaks down, or whatever if they need you and you know they're the types who are good to reciprocate.