Di, I don't know anyone except 1 person who married someone that they've known since high school. That marriage I mentioned ended in divorce after 14 yrs.
My partner is a grandfather. The grandson is 4 yrs. old. He is the parent of 2 grown children. I don't pretend to be their 2nd/step mother at all. I am Chinese-Canadian and he is German-Canadian. Their birth mother is originally from U.K.
I would not expect his children to warm up to me when already I look very different from them and especially, when I was not the woman to raise them from babyhood.
I think the children relate to their mother abit differently than their father. I know my partner fought in court to have equal live-in time for his children after divorce, but as you know the mother wins. Which can be harder on a father who genuinely cares about their children.
At this time, the children get along well with each of their birth parents. My gut feeling is that his daughter enjoys getting into lengthy intellectual discussions with her father vs. getting more woman-to-woman nurturing from her mother.
As for my role/relationship to the daughter...I'm probably just an older, friendly woman to her that can discuss with her about art, literature sometimes at esoteric levels
...and talk with her about her current job where she teaches English as a 2nd language at private to wealthy visiting students from the Pacific Rim countries. She uses me to bounce off her ideas on relationship dynamics between her, as a white, young female teaching to Asians students --young or middle-aged. She has these theories about Korean, Japanese and Chinese students ...which I'm fascinated to hear about differences/similarities. Some I agree, sometimes I don't agree.
Son is similar in terms of a good relationship with father, though he lives in a different province.
Based on what I've seen in past 5 years, it doesn't appear to me, that my partner is getting the "crumbs" in relationship depth with his children. If the children are/become well-adjusted in their own independent/personal lives, it paves the way to a better relationship to each divorced parent.
In honesty, it is less painful to everyone in our situation, including myself, that I don't try to play the role of a substitute parent for the kids.
It's not that hard for me to be in this role..already I'm a happy aunt to several children in our extended family.