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You can't make everyone happy, and you can't make everyone like you. The only thing that you can do is learn from any mistakes that you've made and continue to try and be a good friend to those who DO stick around. Those are the people worth fussing over, those are the people worth fighting to keep.
So! If someone decides that you're not worth their time, cheer up! Hold your head high, and know that you're better than they might think you are... And then spend your time proving that to yourself- and not to them.