Cucumber, You are SO NOT alone!
My relationship with my A wasn't nearly as long as yours, only 8 months of my life, but these last 8 months I became a completely different person as well. COMPLETELY wrapped up in him, HIS problems, HIS pain, HIS life.....
and I became isolated. Lonelier than I have ever felt. Lost the desire to meet new people. Waited at home for him to call. Depression, bad depression. And he went back to his ex wife! He forced me out of his life...and every day I am becoming more and more grateful for that.
I am half way through Codependent No More. GREAT book, a lot of good insight, and really starts to make you look within yourself for the answers. I am also a month into counseling, and it's one of the best things I have done.
You say you want to be the person you once were....IT IS NEVER TOO LATE to be that person. You ARE that person. Start to focus on you, 100% on you.
And I would ask you, what is something in your life that YOU really want to do? For me, I am finally back in school going for my degree. That is my positive focus. And I will do something great with that. What about you? What do you want?