I've been bullied a lot too, mostly by my family. As a child I did well with others my age but the constant abuse and humiliation from my family eventually took a toll and I became super socially awkward by the time I was 16, practically overnight. It just got worse and worse so now adults bully me, outcast me, whatever.
Like others have said, I think people can sense a vulnerability in others. From the way we speak, our mannerisms, just the way we carry ourselves in general tells a lot about a person and people react to that. Once someone on the top of the social hierarchy senses those vulnerabilities, weaknesses, or whathaveyou, and targets us..others will follow suit to fit it and then, suddenly it becomes "okay" to treat someone so cruelly.
Generally speaking, I think people tend to treat us the way we treat ourselves. If we generally think down on ourselves then others will treat us poorly, vice versa. Not that it's an excuse for people to bully others, of course, it's not ever okay.
I'm sorry people have treated you so badly, Mystic. Just know, whatever their poor excuses were/are for bullying you, you did not and do not deserve it.
gsss*