I think it depends entirely on what you circumstances were pre-children.
For me, as a lone parent of one with no support (financial or otherwise) from my child’s father, I absolutely love our life. I’m mid-thirties though and spent a decade or longer going out and getting wrecked every weekend so it’s absolutely the last thing I want to do now. And I’ve made peace with the fact that I’m unlikely to meet anyone romantically any time soon, I’m lucky in that I have family close by that would babysit every now and then if I asked but I really just can’t be arsed with it. I’m happy for all my evenings just being at home, eating far too many snacks and watching crap telly while my LO sleeps. My child is the best thing that’s ever happened to me BUT I was utterly miserable before I was a mum, and hated the cycle of drinking way too much that I’d got myself into, so the only way was up!
I’m guessing that you were quite a bit younger than me when you became a mum, and you’ve already said that being single wasn’t your choice, so I think those two things (plus the fact you have four kids!) are why you don’t look at your life quite so adoringly at the moment. It’s totally understandable and I hope things improve for you soon.
But, we’ve all arrived at single / lone motherhood differently, and that’s why we will all have different takes on it. For some it’s freeing, for others imprisoning.
I don’t have any advice as such but all I will say is please don’t give it hope. I was so utterly fed up with life before I fell pregnant unexpectedly, and now I’m truly content. You never know what might be around the corner, and I do hope it’s something wonderful for you. Stay strong, you’re doing brilliantly ❤️