Horrible teeth. My front tooth is chipped, and my front top are rotting really bad. I made a post in /r/dentistry and they said I had no hope.

I'm pretty sure they can pull out your teeth and give you new teeth nowadays. Don't trust r/dentrist, go to an actual dentist. Most places do free consultations.

Horrible posture. I walk with a really bad slouch. Idk how the fuck I developed it, but I just walk really terribly.

Walk better? This is entirely fixable.

I'm emotionally developmentally stunted. I have thin skin, low self confidence, etc.

Again, this is something that is fixable. The fact that you're cognizant of it is 50% of the work. Now it's finding something to build up your confidence. Part of it is outgrowing this defeatist attitude you have. It doesn't do you any favors and doesn't even feel good.

I'm very scrawny. I'm 5'6" and 115lbs. He said that women will never find me attractive because I'm not "manly" and women want a man who will protect him.

This is stupid, women's tastes vary. Most women will want a heavier guy, so if you want, start weight training. It will not only give you confidence and weight, it will also give you strength and motivation and energy.

I may be autistic.

Socially? You can work around it and learn social skills.

I currently live with my parents because I suck at managing money.

Go visit a bank accountant or a money planner to help give you tools to manage your money better. If it means sticking a spending limit on your debit card, do that.

Look, your "friend" is a douchebag. Honestly, it sounds like he's taking out some anger and issues on you. People with issues sometimes like to kick the weaker around to make themselves feel better.

As it stands, you want honesty? Yeah, most girls probably don't want an awkward guy who is scrawny, has no confidence, can't manage his money, etc.

Do you need to give up on women and go your own way? Not really. Almost every issue you named is fixable.

Why the hell would you go your own way before fixing the issues first?