How do you know who you are?

I've recently come to the realization that sometime over the past few years I've completely lost myself. Or maybe I never knew myself to begin with, since I was a chameleon in high school and generally my entire public school career. This lack of identity is contributing to catastrophically low self-esteem which leads to suicidal ideation and increasing depression, as well as pushing my partners away and not fully trusting them or allowing them close to me. Suffice to say, there are hurt feelings all around and I don't know what to do about it.

I want to do better and be better, but in order to do that I feel the increasing need to figure out who I am. Because after all how can I authentically relate to other people if I don't know who I am at my core. Due to this though sense of self, I lack trust in myself and others. Because it can't trust myself, how can I know that my trust and others as well placed? How can I take them at their word if I can't take myself and my word.

Have any of you gone through this, and come out the other side? I'll be honest, I'm terrified, and I don't know what to do.