Same as you OP.
Being a single parent, even if partner is not home much is ABSOLUTELY not the same.
Even if they are of little practical help during the day, they
- Earn money
- Help with decision making
- Share the burden of responsibility for keeping on top of things like mortgage renewals, insurance, car servicing, bills, school choices
- Share joyful moments
- Are there for things like Christmas
- Are usually there at the weekend
- Often do DIY jobs
I do all of that, and the "invisible stuff" is the most stressful. Dealing with a sick child, panicking about whether to take them to hospital and nobody to talk to or calm you down, dealing with crap at work and nobody to vent to, worrying that if I lose my job, I will have no money, feeling unloved and unappreciated, making some parenting choices without anyone to think it through with, being ill myself, the utter dread of what would happen if I was incapacitated or worse.
There are of course upsides, too. I focus on those. For me, they are:
Look at you're beautiful children. You did that all by yourself.
You are a phenomenal role model.
There is no "adult to adult" conflict at home. Bliss.
You can eat what you fancy, watch what you want, go to bed when you want, have friends you want.
You are not undermined by another parent or played off against partner by the kids.
You get very close to your kids.
Appreciate those are my personal examples, others with and without a partner will be different.
I have had a lot of counselling to arrive at a place I feel Ok. It takes time and I have lots of blips when I feel just like OP.