Hi OP, my mum was a lone parent, like you not by choice. But the hardest thing for us was that every so often my dad would show up and be horrible all round. If your partner doesn't want to be there, that's terribly disappointing, but in the circumstances you're better off without him.
It can be done. It wasn't easy but my sister and I turned out alright and ny mum has a restful retirement now.
Do insist on maintenance from the father, don't put him on the birth certificate, and find someone to talk to IRL.
You sound like you think fate is punishing you, and deservedly. None of the horrible people I've ever known admitted to being horrible. I'm sure you're not that bad! And anyway plenty of awful people have nice lives, there is no correlation.
As for being a failure, what's the world coming to if practicing dentists claim to be failures? I think you can safely lower your expectations of yourself. All the best!