Rather than concentrate on the selfish part, which I know is easy to do, I think it's more of a situation of dysfuntion breeds dysfunction and the self-centered trait is just a symptom of the dysfunction. My husband, who is an only child, was also very self centered, alcoholism just brought that out even more. His parents are also very self centered and self involved. There is addiction going back generations. Also not surprisingly, his parents were his biggest enablers.
But I also agree with lillamy, regardless, you deserve better.