I'm not sure how qualified i am to answer this post, when i got approached by google i didn't actually reply because i'm 99% sure i wouldn't even have got to a first phone interview so your way ahead of me in employability already.
But i've had enough canned responses and no responses to job applications or redundancies from startups going tits up, failed promotions or the right thing said at the wrong time and vice versa to suggest the following:
a) Never ever take rejection personally, learn what you can from it but definitely don't beat yourself up over it. I know it's easy to say but in the first place it's obviously downright unhelpful, in the second, there's just so many ways from the apparently sensible, to the outright stupid, people come up with to reject you it's unfunny. There's probably a good reason half the time you get no feedback at all. A number of factors are out of your control. A number of them involve prejudice and herdthink. A number of them involve people making mistakes, politics, or having bad days, asking the wrong questions or just not happening to ask the right question that would make you shine over the other person. A lot of them, e.g. they found someone better, don't even involve you not being good enough to do the job anyway or are just luck, taking a path through domain A rather than domain B, not having buzzword X on your CV when your otherwise excellent CV got binned by someone non-technical in HR.
b) At the risk of getting too metaphysical, quite often it's very difficult to know what the job's actually like until you've started it anyway. So the fact you didn't get it might not be as big a deal as you think (putting to one side your current one sounds far from ideal).
Obviously a lot of these are mistakes you wouldn't expect a decent employer, e.g. Google to make, so the fact you got to a final stage interview with them must put you in the top small fraction of the population anyway so don't take that for granted. And on the flip side, given the fact Google have just come to the conclusion that great exam grades don't necessarily mean great people [sure this popped up on HN recently] just shows how random it can be.
c) Obviously farm your cv around as much as possible to friends, other people in the industry on here etc. for feedback. Hone your technique. Don't give up on google, i gather a lot of people fail on first attempt but get jobs after reapplying later on.
d) Applying for jobs, always reminds me of going through school/college/university. Loads of my friends dropped out at various points, got labelled stupid, unemployable etc. etc. but have since gone on to get one (or more) degrees, MBAs, very highly paid and/or very technical jobs or possibly average jobs that they are just really happy in. The one thing that unites them is that they didn't give up even if when things seemed pretty hopeless and then took one (sometimes very small) step at a time.
Good Luck.
As an aside, obviously your current work situation with long hours isn't helping. I'm assume you have to be aware of the general consensus (mythical man month, agile/xp, amongst many) about how counterproductive repeatedly working long hours is. I'm not sure i'd necessarily go as far as quitting if it's possible to salvage the current job with more sensible hours, a break, go part time etc. or even just work contracted or sensible hours and make them fire you. Though often in these cases it can be the person themselves contributing to the pressure, through fear of failure, perfectionism or just taking onboard other people's monkeys (One Minute Manager Meets The Monkey) and they find kicking back and just letting some stuff fail actually works out better in the long run.