Why do I feel so much pain ? :'(?

A couple years ago, I went to a school in middle school, and back then I was very outgoing so I just dove right in and made a bunch of friends. Long story short they all decided they hated me and turned against me, and it was one of the worst experiences of my life. My self esteem plummeted and I shut down socially. This was two years ago, yet lately I've been feeling the pain of the rejection strongly. I don't talk much to anyone, and whenever I try to open up to anyone about how I'm feeling they don't understand. I feel like not a soul on this planet understands. I actually think I might be dealing with depression because I've been having suicidal thoughts although I'd never commit suicide. It's even ruining my relationship with my boyfriend because I made the stupid mistake of opening up to him and telling him what I was going through. How can I fix that?What can I do? Why does this hurt so much?