I've got a couple of angles on this, I hope it helps.
My parents seemed very happy (from a child's perspective) but then when my older sister died when I was 10 they sort of lost some of the glue that held them together (she was severely disabled)and started doing their own things more. From then on I remember them as two separate people - we had a family holiday once a year but all other stuff was either one or the other of them. I have happy memories from before this time though, when we were a unit, that have shaped the way I want my children to experience their childhood, so there's a positive from being together. But I think they were happy then so obviously that's the key.
Then they just became really different people. For about six years they carried on like that, together but separate in the same house, for my sake (my other sister had moved out by then and was older so probably has a much more accurate depiction of it. The outcome was that they were so wrapped up in themselves (and their grief probably - which may have had more of an impact on me than them staying together or not, if you get me) that I developed major attention seeking tendencies which I still have and which still seriously affect my marriage and behaviour. I am a great partner and mother in that I am good company, I do not nag, I am loving and affectionate and I fully support my husband in everything that he does, but I am very very demanding, erratic, do have depressive episodes and fall apart if he is not affectionate enough in my view, go off seeking attention elsewhere in a rage, regret it, etc etc. And I honestly believe that that is where it has come from.
Had they broken up earlier, it would have been awful, but much much clearer and there would have been less of this horrible dark time when nobody spoke to each other. My adolescent/teenage years were horribly lonely and I fell pregnant at 17 which was when they finally decided to split up, but that was the first time they properly spoke to each other in ages - to talk about me being pregnant.
Here's the point: the actual break up has affected me and my other sister quite badly. We can't see our parents together as adults, we are not quite sure what happened, and my mother clearly has massive issues that she hasn't dealt with.
BUT
They have both got partners now who they have much better relationships with and have challenged my view of what a partner/wife/husband should be and are ultimately happier people.
In my view, a happy single/remarried parent is miles better than two parents that are miserable. Children will adapt as long as the new situation is happier than the old and they will respect you for your choice. (My dd1 at age 11 made me cry the other day when she said she was so impressed with everything I did when I was 18 and a single mum - I had booted her biological father out when she was 4 months old because he basically just didn't give a toss about either of us). I am now married to the man she considers her dad and she has high hopes for her future relationships 
If you stay in a relationship with a person who treats you like shit or barely speaks to you, or trashes your confidence, or whatever, all you are doing 'for your children' is showing them that it is OK to put up with this, that this is what they should expect from their future partners.
We work work work at our marriage, despite our (my) faults, because I want my daughters to grow up and FULLY EXPECT to have a man/woman who respects them, treats them well, is affectionate, supports them, etc. I will not allow it to become some sort of facade, or allow myself to become submissive. I speak openly about our arguments (within reason) to my children and I let them see us resolve things because I NEVER saw that as a child. I saw destructive feelings that were not dealt with. However, I would leave if our relationship went to shit, because I want them to know that whilst working at it is important, you do not have to stay with someone who makes you miserable.
Sorry what an essay.