Hi Eden,
Two things:
One: i used to have a lot of negative thinking because of my mother's "training" (she had negative thinking and anxiety, she was a kind of narcissist, as well, as a defense from a very painful childhood). I still do but I can manage it. It is possible. I know, it is not easy at all.
Two: when you feel comfortable, you can talk about the bad things you did in the past, this is an anonymous place, perhaps it could help you a bit.
I have had the help of therapists but sometimes I have progressed by myself by various means. At certain point , removing myself from the environment I was in helped to see things in perspective.
Ok, hope you keep posting and feel better soon