Oh my goodness, I know what that feels like too! And I have a theory that deep down inside, everyone just wants to be accepted and loved. No matter how proud they may act, or how much it may seem like they have it all together, deep down inside of every single human being is just longing to be loved and accepted.
What I've found helps with battling that feeling is to go out and find someone who feels left out (you won't have to look far to find someone) and give them the love and acceptance you wish you had received yourself.
But always remember that you are very much loved and accepted here!