Well don't go back B, go forward. You can do it. We all want to see more of that dynamic, wonderful person inside of you. This is a very interesting thread, and one everyone has thoughts on I'm sure. I don't think being a melancholy or sad person has as much to do with environment as we may often think. I had a near ideal upbringing and I still experience many times of near depression and intense sadness.
Perhaps some of this ties into being very empathic. Not to downplay peoples difficult lives and upbringing, but we are all predisposed to feel sadness in a certain way I think. In many ways it's human nature to want to experience it--at least that's how I feel about it. Look on any poetry site and the "Sadness" category is always one of the top two.
I've also noticed (as Enty has commented before) that my creative juices really flow when I'm sad. I don't know that this says I prefer this state; I thinks it's saying I want to better understand this state and thus relieve it. But I am definitely in a much more analytical mode when sad, much more questioning, than when I am happy. During the periods of happiness, I just want to be (to experience it). Also, during happiness I record and store emotion, during sadness I analyse it. I really want to understand it. I think when angry I experience emotion at it most raw form, this is the state it can really get away if you let it. But we all need some sadness I think to help balance things out. But we can't live in it; we can, and must, learn from it.