I don't want to sound unsympathetic, as you seem to have an actual medical condition that's substantially impacting your life. At the same time, I want to point out a few things that really struck me reading your post, as I don't think mindless sympathy is the ideal approach to helping others. (Asperger's has its upside, too... :) )
"essentially told by HR that I was obligated to comeback full-time"
BS! Indentured servitude has long ago been outlawed in the US, and while my company generally tries hard to get our good interns to come back full-time, HR doesn't phrase it as an obligation.
"my girlfriend of 8 years (seriously, we had been together since we were 16) had just left me because I was exhausted and working all of the time"
There's an awful lot of relationship "turbulence" in the mid-20s, and it's awfully hard to pin a breakup to a specific root cause, especially when it's fairly vague.
"I'm actually afraid to get another job."
Why? For a good coder, they're everywhere, easy to get, and pretty handy for paying the bills.
There's an substantial chance that your prior employer is just a grind 'em up and spit 'em out crappy employer, though it's hard to say from only hearing your side. But if it really was "your employer's fault", then getting another one has a substantial chance of fixing a large part of what you are complaining about. (And if it was really "your fault" (see below), getting another one gets you that one step closer to figuring that out too, so that you can change that.)
I'd offer a couple pieces of advice:
1. Take responsibility for choosing your own path. Don't let HR tell you you're obligated to come back. Don't work for crappy employers.
2. Don't "double down" on your limitations. Given that you have a legitimate medical condition, don't tie other aspects of your life to that condition. Don't blame a failed relationship on it, etc; otherwise, you're liable to fall into a victim mentality, which regardless of whether or not there is a true linkage, doesn't help you to make thoughtful choices in your life.
3. There are plenty of employers out there for good hackers, and I've worked with people with far more messed up sleep/work schedules than you, and I'd hire (some of) those people with nothing more than a phone call telling me they were available.
If hacking is the one thing you love doing, do that. Going to academia, or anything other than hacking, is a cop-out.
Go get another job hacking, and if that doesn't work out, go get another job hacking, and repeat until you find one that makes you mutually happy. If you get to 4 or 5 and find that you're still "0 for", then think about whether there are other root causes, and whether you bear more responsibility for some of your challenges than you are currently admitting to.
You need more data. You came to HN asking for it. IMO, you really need more data about YOU and how YOU will handle your life responsibilities, and while you can ask HN how people here handle their lives, ultimately, it's going to be a lot more productive to find YOUR answers in YOUR mirror.