I'm going to offer a counter-point to your suggestion:

I don't believe changing the external environment, or income, or people who you are near, is going to do jack shit.

Here's why: I feel exactly like the OP. Failed weight loss. Failed relationships (in my case it's making good friends / co-worker relationships). A giant list of failed or incomplete side projects. Still can't pay off my loans.

The difference: I make 3 times as much as the OP. I work for (and have always worked for) exciting startups. I live in a trendy area of NYC (not SF, but the same health-minded social stuff).

The money, the atmosphere, the location: false hopes. They don't change you you are. You're not your salary. You're not your neighborhood. You're not your job.

YMMV, but as someone who's been-there-done-that and hoped that a better job, more money, and better location would somehow fundamentally change who I was, I think that line of hope is no different than someone who thinks a bigger TV, fancier car, or hotter wife is going to make them happy. It won't.

EDIT: Let me be a bit more specific. I don't like it when people do some hand-waving and claim that it's just The Way It Is.

The main issue is that your environment does effect you, it just doesn't change you.

Money: I've lived on ramen & water. I had friends who understood that drinking cheap beer at home was the best I could do. Once I started making more money, I certainly thought I could avoid spending more. And for a while, I did. But things start to add up. First, you network with people who make the same Good Money that you make. So you pretty much have to up your entertainment budget or else be a recluse. Like it or not, your old peers will envy your money. You'll stop getting invited to basement parties (age is certainly a factor too). You decide one day you deserve better than living in a slum with bars on your windows and doors and rats in your walls and upgrade to an OK apartment. You decide it's time to "grow up" and stop buying used clothes. You decide Natty Light isn't the best beer in the world. Your old $25k/year lifestyle is now a $75k/year lifestyle with only incremental changes. This leads me into...

Location: If you move to a yuppie place, you'll spend yuppie money. Coffeeshops cost more. Old dirty grocery stores give way to Whole Foods. There will be subtle, almost subconcious pressure to spend more and be even more critical on yourself than you already are. The "keeping up with the Jones'" cranks into high gear. If you feel like a fat loser in the midwest (or wherever), it's 10x worse when you're surrounded by wealthy in-shape people. Trust me. My smug sense of being better than most people when I lived in poor suburban/rural areas has given way to feeling like a worthless fat piece of crap every time I walk outside (this is a bit of an exaggeration, but with a BMI around 30 I'm easily the fattest guy I can see 95% of the time).

And finally, job: A job is a job. Some are better, some let you work in your boxers, but from 10,000 feet they're all just ways to give you more money to spend on shit that you hope makes you feel better but doesn't. You can try to derive happiness from a job and for some people it works, but it never worked for me because I don't really have much control over my job. At 25 years old I'm not yet in the position of actually making big changes. Sure I can decide on a framework or the language to use, but do I choose which direction the company goes? Do I make hiring decisions? Not yet. Certainly in 5 years this will change but at 3 years out of college, even in startups, you're not given the sort of responsibility, IMO, that gives significant job satisfaction.

Anyway this is all just IMO. There's certain to be folks with the exact opposite feeling on this, so I'm not claiming I'm right, just that this is my experience.