OP; you are right of course; some split up families have it easy. So do some together families. There are so many different circumstances, and all of us when we are down look at the positives to other people's situations, and wish....
I am very lucky. I am a single mum of 2 kids, who are 3 and 4. Their father comes round occasionally, often when I have nagged him about it, but would be utterly bewildered by any suggestion that either of them stays with him for a night or weekend or anything - DS has asked if he can go and see dad's house one day (he knows we used to live there, but he was very small when we moved out) so obviously pretty far from the norm. He doesn't contribute anything, but he was pretty expensive when we were together so I'm better off having moved out anyway.
Because of where I live, I can afford live in help, and I have been lucky enough to find an amazing one. She isn't perfect; nobody is, but she makes my life so much easier. There are times when she (or the 'being an employer' part of my life) drives me crazy; but there are times in everyone's life when they are driven crazy.
I had a friend here whose husband was working 6 weeks on, 2 off, in Afghanistan, so she was on her own with the kids for 6 weeks at a time, without help at home (she didn't work). She had it much harder than me, and though I miss her, it was absolutely the best thing for them as a family when he found a new job somewhere they could all move to.
But there are disadvantages, even to what I know is a 'lucky' situation. You have a responsible co-parent to discuss your kids with; you have a partner to love and who loves you - don't knock it :)
I don't think you ever said 'all' split up families have it easy; lots don't (I'm guessing most don't), but I'm not the only one I've ever known who has not had to struggle too much, even if I am the only one there when the kids throw up all over everything in the middle of the night, yet again. But everyone's situation is different, and I'm not sure why you should mind more that split up families have it easy than that together families have it easy? Anyway I'm sorry you are having to deal with what you are, and hope it gets easier for you soon.