@Readandwalk
How would it work for non adult SC then? Me ringing up their mother who've I never met and saying can I take your children to my new home? No I no longer see their father. Yes I know they already have two homes but can I add to that, with your permission by having them stay at my home once a week. As a non relative with no relationship to either parent.
See it's really really messy.
Exactly this.
My DSD was conceived during an FWB arrangement - DH and DSD's DM were never in a relationship together. DH was engaged to his exGF previously to meeting me and our subsequent marriage, with a relationship lasting from when DSD was a baby until around 5. DH's ex was understandably super attached to DSD - a very cute baby / toddler at that time - and did naturally undertake a maternal role with such a young child.
BUT, DH and his ex split when DSD was 5. DH knew at that time he was likely to date again. So what do you do? DH's ex wanted to maintain a relationship with DSD, and DSD also wanted to see her - she was only 5 and they had a strong bond. But both DH and DSD's DM both agreed this would be confusing in the long term for DSD, once DH met someone else / had other relationships.
Similarly, DSD's DM was engaged until last year - her DP taking on a step-father role and living with DSD for a number of years. Again, now that they have split, contact has been cut between him and DSD - not necessarily at the choice of the step-father, or DSD.
It's unfortunate, but right that it's way too messy in most cases for step-parents or acting step-parents to maintain contact with their child DSCs, regardless of strength of feeling - and realistically it's not up to them anyway.
For my part, if DH and I divorced, I would not expect to maintain a relationship with DSD - much as I would still like to know how she is / what she's doing.
In terms of our relationship, I try very hard not to 'parent' - she has a mother and a father already and doesn't need me butting in, I very much try to respect that she already has a mother, which helps avoid conflict between me and her DM. So I don't do parents nights / hardcore discipline etc. But, she does live with me and DH 50%, so I do organise fun family activities / family dinner chats / advice / cuddles / love you & love you too's, and I do feel comfortable chastising her or setting rules in my home without necessarily consulting DH. If DH and I separated and she initiated further contact when she's a bit older and had more choice, I'd be delighted to see her and would never turn her away if she needed something.
For those without step-children - would you expect to still see your mother in law, or father in law, after separating with DH? Or nieces and nephews on DH's side? If you couldn't, would you be sad, or completely devastated / heartbroken? On marriage, they become your family too - much like step-children.
I'd expect it's not like losing contact with your own child - more like losing contact with an in-law that you have a particularly close relationship with. Quite sad, but expected on separation with DH, and most of the time for the best for all parties moving forward.
As a final point - I consider my DSD my DSD, but I don't have the strength of feeling for her that I would for my own biological child - I think that's likely to be vilified here, but quite natural. It doesn't at all mean I don't care for her.
Likewise, I'm sure she sees me as DSM - she likes / loves me, but not remotely close to the equivalent strength of love she feels for her DM. Again, natural!