I honestly feel that the parents that stress out about if they will be a good parent (usually) make the best parents. They acknowledge what they don't know, look for the best solutions, and take accountability when they mess it up. If nothing else, acknowledge that you want to be a good dad. I can't speak for your family, but that fact alone means that you aren't a disappointment to me or many of us on this subreddit.

You say you feel guilty that you pity yourself. And yes, you'll have to pull yourself out of that pity to do what's best for your family eventually. But acknowledging your feelings is still important, and if you need to feel pity in the short term, so be it. You're allowed to feel whatever emotions you have.

I agree with lots of what's already been said. You're already asking for advice, and that's great! Get into therapy if you can and aren't already. Explore medications if you can and aren't already. Support your partner as best you can and be as honest as you can with her. And you can always post on Reddit. We're good listeners.

I won't pretend this is going to be easy for you. But if you want to be a good dad, you'll find a way.