Being a single parent is hard but that's ok. As long as you know you are going it alone, it's just a matter of prioritizing and keeping on a pretty predictable schedule.
But when you are in a relationship and it feels like the other parent has checked out, then you're a single parent but with a partner who may or may not give input...and you never know they will give input. It's impossible to make a schedule or if you do and just do your thing, then they get pissed off because you didn't "ask" them.
It's kind of like walking on eggshells all the time. You don't know when they like or don't like a decision you've made and if you point out that you asked for input and they didn't give any (btw, NOT giving an answer implies agreed consent to whatever I decide), what do you do?
I sure miss my partner.