I can think of a million things to say, but the single most important thing I can think of is to read this book... https://www.amazon.co.uk/Book-Wish-Your-Parents-Children/dp/0241250994
I appreciate you're down, depressed, struggling, but you have the power to be better than your parents. Bad parenting passes down generation after generation, but at some point someone has to take a stand and do things differently. You can be that better person.
It's not easy, but you can take control of your life and make it better for yourself and your new child. Take baby steps towards a better life.
The most important thing I can say though is, take care of yourself. If you're not well yourself, you won't be able to take care of a girlfriend or daughter. Focus on you first.
Good luck friend,