What makes a person selfish?

My family told me I am selfish because I am trying to end a toxic relationship with my husband. I have always done everything what my family asked me to do except this one. I have always supported my parents mentally and financially, even when I was financially not so strong. And now they are saying me I am selfish, that I don't love them. They think their reputation in society will be damaged because of my decision.

After hearing this from my parents, I have been thinking a lot. What are the characteristics of a selfish person? If I want to take a decision for my life, for my future does that make me selfish?
What makes a person selfish?
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