handforther Things were so much better for my siblings and I when my parents finally fully separated and we lived with a stable parent where we knew what to expect. It wasn't always great, we were shaky as we all had our own traumas from it, but it was so much better than the eggshells and pain of them together or with my mother.
The issues came when he started to bring his dating life and new partners into our home. He was a very people-pleaser person so any new partner brought into the home meant things were changed to accommodate so the expectations would change depending on whether the new partner was there or not. His dating tended to involve drinking - he's a guy who likes a party - and that made him less stable at a time when we needed him to be as stable as possible. At first he kept that out of the home, but once we were all living together, it was part of my life again in a way that left lasting harm. My siblings and I all started acting out and I became very dysregulated when the extended family started taking and putting up photos of us with the girlfriend as a 'family', it lead to a lot of issues that decades later my father and I can't really talk about. He thinks his family 'forgave' him and what happened with my mother, I think they erased it to make it prettier. We may both be right on some level, but I think when there is potential trauma involved, helping a child feel secure in reality is very important. New partners and adults acting as parents are a risk to that.
I was happy for him to be dating, told him so, but I was happier and more settled when his dates had as much affect on me as him going out with work colleagues (which he may have been shagging, who knows, not me - and that's nice). No one expected me to defer and like his workmates, they might change our schedule now and then, but they weren't going to tell me off for getting angry about it. I only had as much knowledge as affected me and no more - no one expected me to care about that.
As someone who was 'included' in way too many adult things as a child, I felt more loved and considered once I was just living with just my father and seeing him do things that made him happy outside the home that I was mostly not included in - it kinda gave me permission to do it too after a long time where it felt I couldn't. It was really depressing when that was taken away because when and where we were, 'moving on' and making a new family was seen as best for children. There was no moving on, my mother is who my mother is, but I was able to move forward a lot more easily once I could have stability and space to process my feelings without external pressure to feel any sort of way. The partners being a parent delayed that, I had terrible depression in the last year with them that everyone thought them marrying would help, somehow.
I know others who the safest option was moving in with another adult right away and were really careful about the impact on the child. I think it can be done, but it's difficult to do well. I think it's important to recognize that challenge and that even things that seem simple - like photos - can have a bigger impact on a child and their sense of safety than adults often appreciate. I think new adult relationships come as they do, but how that person is to the child is something entirely different with a lot of factors to consider.