Have experienced this from both sides. My parents separated when I was 7 and it was the most painful thing I had ever experienced. I used to go to bed praying that I would die in the night (this was when I was about 10 by the way, so the trauma went on and on). To be fair, my parents had enormous problems and did not handle the separation or divorce in anything approaching a mature or responsible way. When I became a parent, I really started to understand that they had written the book on how not to do it.
That said, I stayed in my marriage trying to sort it out for over 6 years because I didn't want to put my children through what I had been through. I have to admit, it has been much more painful to put my children through it than to experience it myself. It doesn't help that those 6 years drained me of all my personal resources so trying to do all this on an empty tank, so to speak.
DCs are 12, 9 & 5. DC1 was already having counselling and this has helped support him. DC2 is now having counselling at school. She is struggling and feels very insecure as she has always been a challenging child and now feels that she makes life difficult for everyone. DC3 has started bedwetting. School have been fabulously supportive of my DCs, noticing when they have been a bit withdrawn and offering support appropriate to their age and state.
DS1 has had nightmares about the separation which show that he understands, possibly better than me, the dynamics in our relationship and how unhealthy they were. But this is challenging for a child who still sees the world in black and white.
That said, it is only 4 months since we separated. I was fine to start with but hit an emotional wall recently which has made supporting three distressed children difficult. I do see signs that the children are adjusting - each child has periods when they can be lighthearted and play. They are beginning to play with each other again without arguing (which is how they were prior to the split).
My DD made a point of telling me she enjoyed Christmas (she had said she didn't want and presents, what was the point). Have checked with other 2 and they had a good time too. she also loves her new room at her dad's house (we gave them each a budget for new stuff which gave them a real feeling of ownership).
But this has taken a lot of work and even more self-sacrifice. We went to ex's for Christmas lunch with his parents and spent most of Boxing Day with them too. I have seen friends with ex, we have hosted events together. I do not find this easy and know that I need more distance but I feel it is important that the DCs see us both loving them together.
I don't think my DCs will ever feel as secure again, I think they will feel sad about this, probably all their lives. I hope that, when they are older they will at least understand why. I am hoping that we can support them so that they learn to live with the situation and appreciate the positive things which have come out of it. For DS1 this has been discovering how many friends he has, for DD it has been styling her new room.
I would rather we hadn't separated but once I realised he wasn't sure he wanted to be with me I couldn't pretend any more and, quite frankly, I think I deserve better than to be with someone who isn't committed. Even if that means being by myself.
Sorry so long! But it's not a simple question, is it?