*All of this. ^
Add onto this being the one driving the kids around to every hobby club, extra curricular activity, and every friend's house, and also every dance lesson, sports activity, kids party, clinic/ doctors/ dentist/ hospital appointment, and parents evening.
You either have to hang about for 2-3 hours while they're there, or drop them off, drive back home, hang around for 2 hours, and then drive back to get them. Half your free time is spent running the kids about (and running other errands,) if your partner doesn't drive...
Same with visiting relatives - yours AND his, and going out for takeaways, going on day trips, having to go to hospital appointments, having to fetch your DP from work if they miss their bus,...... There are loads of examples...
*
I am with you.
Luckily my ex didn't become the father of my children. I can only imagine the load that would have brought.