Seems like people spend a lot of time not trusting you/trying to figure you out so you don't get to TALK a lot or let your feelings out. Plus it's hard to trust people.
You trusted your friends and they helped the bullies hurt and betrayed you... so it's hard for you to trust new friends. Is there anyone at school or in your community who is your age or older who is nice? (Besides Uncle who you miss)
Is there any way to talk to your Uncle ? I bet him not being around when he was someone who supported you/like a brother really makes things hard sometimes.
You also mention that you remember your past and it makes you lash out/get angry - do you just mean the students at school who hurt you? Is there anyone else hurting you?
You have a hard time letting your feelings out and you could take a lot of pain and stuff it down or hide it from family or other people (when you were a child you said you were the guy who could "take a lot of pain") but now all that pain is still in there with no outlet.... and you feel really angry all the time
(or depressed) so it comes out in hitting or getting angry or losing control (or hurting yourself)?
Is there any physical activity that you like to do? Is there any thing you can think of that has ever helped you to let go of some stress or tension or anger? (Like running or punching a punching bag or martial arts, sports, games, working outside, art, etc. etc.) ?