How do I genuinely change own personality to become less self-absorbed? Should I fight for a second chance?

This has been the cause of the end of a relationship for me. Even though it's almost been a month, I haven't been doing so well. It has been because I'm a very self-absorbed person, and I don't doubt it. My dad has said the same thing about me while I was feeling the effects of Seasonal Affective Disorder. My psych assessment identifies me as a person who lives in isolation and prefers to live in isolation. I don't doubt that I'm an isolated person, except I usually want to have a special someone in my life. Even beforehand, I've acknowledged that I'm an introvert, and I usually enjoy time for myself.

What are the ways that I can take to genuinely become less self-absorbed? By that, I don't mean the list of things I should do when interacting with people. I want to genuinely change myself, so that my lack of self when interacting with others is as natural as possible.

Also, about this relationship. It was last month on the 23rd of December that she told me she had enough of her own personal problems that she couldn't handle the commitment, but still loved me. It was until last Tuesday that she no longer expressed such feelings for me. To be fair, I kind of blew it. I was being my self-absorbed self, and tried to tell my problems to her, despite her already having enough of her own. Ever since, she has denied the feelings she had for me were true, and I really doubt it. She has been telling me that she's a sociopath incapable of love. Somehow, I've been the exception to that during the months together.

How could I truly transform myself into a more selfless person? Is it a good idea for me to fight for a second chance?