You are their aunt. You were, are and always will be.
With families, it does not have to be blood, it has to deal with the relationship. Bonds with 'official' marriage part is just silly. Marriage is not needed to become a family/create a relationship and lack of (divorce) does not mean that you are no longer part of that family / relationship. My kids have aunts and uncles that are purely family friends.
I do have a daughter from my 'college' marriage. We have always referred to that side of the family as her other family, her other mom, so forth. We have for 13 years of her 15 year old life. I have never ever thought that because I and her father were divorced, that anything would ever change with her relationships. Actually, I wanted her to understand that she was twice as lucky to have so many people wanting her in their lives. Twice as many aunts to love her
