They both raised you. Your dad from birth, your stepmom from age 10. And after your mother’s passing she became the only parental figure in your life. I can assure you that makes a difference in the sense of responsibility one feels for a child, even though it’s brought by very sad, and unfortunate circumstances.

She may not have the same kind of love for you as she had for the babies she bonded with since day 1. But it doesn’t mean she doesn’t love you dearly. And even though you are not her child, you are the oldest child she raised. And being her daughter’s sister matters too. You are a piece of the man she loves, and of the child she brought into the world with him. The first that went through many of the child-milestones the family experienced. Your place in the family is yours only.