Unfortunately I am not a good example of positive coparenting. However I have a colleague whose husband cheated on her and is still with the woman. They coparent really well. She talks to the girlfriend and her husband, they recently all went out for dinner for one of the kid's birthdays. Hats of to her, she has really had to prioritise the kids and put them above her own feelings. Over a year later and she is now at peace with it.
Another friend, 25 years ago, her husband told her he was gay and had cheated on her. He went back to his home country and left her in England with a hefty mortgage and 3 kids under 10. She really struggled, in the divorce she gave up lots of things to keep the peace which put her financially in a horrible place, and never received CMS as he wasn't in the UK.
Now, her and her husband are very good friends with her ex husband and his partner. They all go out the four of them. They do things with the three kids, their partners and the grandkids. Her point of view was she sacrificed alot to keep the peace, so that when he did return to England to see the kids she was always pleasant and supportive even though it killed her.
Now I obviously don't know the men's side in these situations. But from the two women I can say that both have had to bite their tongue, accept they can't control everything, and when new partners came into the picture it definitely changed rhe dynamics. Most people aren't going to be okay with having to be so close to your ex.
Honestly, I think spending every Christmas, birthday, having family time... I don't think it will always be that way. I think new boundaries need to be put in place, not just for the adults, but so that the kids understand their parents aren't together and won't be getting back together.
But I think it is amazing when two people coparent and their kids come first. That was my wish so I understand why you would want it.