Dude, I feel for you. A lot of the bros here have given some
very spirited advice.
Not just in poly, anywhere u are, friends come and go. Don't take
this whole thing too seriously. You sound like you are very much in
need of a belonging and without it, you are miserable.
RELAX man! If the group does not treat you as part of the clique
anymore, accept it and move on. If you are alone while everyone
else has friends so be it. Don't give in to peer pressure when it
contradicts your values!
Meanwhile, move around and merge into other cliques. Get active in
your clubs! But don't look for friends just because you NEED them,
that's a bad mentality.
Relationships are weird, when you look for love/friendship, the
more you look for it, the more it eludes you. My 2 cents of worth
of advice.