I am so bitter about my past that I can't move forward?

It sounds horrible what happened to you but the last you want to do is let your past get in the way of your future. It is clear that you did not have a good time in high school and growing up as a result of your cousin and best friend but you need to just move on from that. Yes killing them is not an option here but there is something you can do. Do not let them determine your future. You have already given them enough but its time to take it all back. prove them wrong in whatever they said. It is all about changing your mindset,the way you think,the way you see yourself and this will establish how others see you.Stop dwelling too much on the past and what could have been and change the 'now' and establish what can be. Start to build your self esteem. draw on the strength of your other good friends. Stop being so hard on yourself and giving yourself a hard time for staying in those relationships with them. You were still young and vulnerable. But as you grow older you should learn to let the past be in the past. You still have a long life ahead of you. And as for the girls, i'm sure they are still there so go for it. There is no reason not to pursue them or any other girls you like for that matter.