Confused about how Lily and Vivian are Chuck's Aunts
So I've gotten to the 4th episode of season 2 and I know Lily is really Chuck's mom. But what i don't understand is how they were originally supposed to be her Aunt's. So Vivian was engaged to Chuck's father but Lily slept with him and got pregnant. The father told Vivian that he had cheated on her with someone else.
So how exactly were they considered Chuck's aunts if they weren't related to her at all? And why would Vivian want to be associated with the man who cheated on her and the child that was the result of that cheating? I feel like I'm missing something. Can someone please explain this to me?
All I want is someone who'll warm me when I'm cold, feed me when I'm hungry & maybe take me dancing