I'm a happy SM. DH is a happy SF. We have havent had the easiest of relationships with our exs so certainly hasn't been without out challenges. We have a child together.
We don't take the not my responsibility approach in our home. We see them all as our responsibility financially, time etc. We didn't get worked up about who did which child's washing or dinner. Or who had to do a drop of and collection. We just saw it as give and take.
Ours are young adults now. They still want to spend time with us for family dinners, holidays etc. We have great relationships and fun with them.
We do mixes of things with each of the kids individually and together. We have no problem taking time away from each other or them. If the kids were all here when younger and the other had to go out or had plans. They stayed and just got on with what ever we was going on in the house.
We take the this is how we do things in this family approach. That took awhile to stop being so impacted by the behaviour of our exs. So did the competitive nature that comes with parenting. We just said we didn't want it in our relationship.
Once we did we just accepted early on in our relationship that our family life would be busy, chaotic and challenging at times. We don't take things to seriously or get wound up by the little things and laugh alot.
To support that we made sure to have alone time. With plenty of ranting and some swearing with alcohol! I actually think like any relationship with children it's important that you invest in quality time together. For us we just learnt over the years to make the most of the time we could have just the two of us. That actually was much easier before we had our dd because she is resident with us full time.