Going anon as I can't be sure whether the people I refer to read this or not.
I'm also not really sure what point i'm trying to make, but i'd like to share my experiences.
OP I empathise fully with you. At uni i've found it very hard to make some real friends. I get on with people fine but i've never really felt that I actually fit in with them, I always feel a little bit like a spare part or the 'hanger on'. Mainly due to similar experiences in the past of being left out of things (whether intentionally or not), which means I do have tendencies to feel paranoid at times. There's also a particular girl in the small group of people I see who is incredibly rude (I think this is only if she decides she doesn't like you or whatever) and belittling. However i'm trying not to let her bother me as there are some nice people that she is friends with who I also get along with. I don't really socialise with these people outside of classes (and I really don't have a great desire to either.. see my next para) so that may be why. I'm not unpleasant or loud, pretty chill really. But.. yeah.
However, I do have other friends from another community (online) and i've got to say these have come to be some of my best friends i've ever made. With them I feel that I am valued as a friend and I feel at ease enough to open up with them. It sucks that most of these people live all over the country and I get to see them in person maybe once a month at most. I guess because of this I haven't put so much effort into making solid friendships at uni, but it doesn't bother me too much. I just get on with things.
I suppose if I had to offer some advice it would be to not let those who shout you down get to you. I'm lucky that I have an outside group of good friends, but I advise you get out there and join a club at uni/online community of people who are into the same things you are.
Don't waste your time on people who put you down or make you feel bad about yourself. I'm not saying don't try at all with the people you consider friends, but don't let yourself be a pushover. If they are your friends, they will make the effort to see you/talk to you. Anything else is essentially an acquaintance.
Apologies for the rambling post, hopefully the OP will know where I am coming from.