I'm going to be honest with you, just going to be honest. After your original post I felt sorry for you and was going to be rather encouraging, then you pull out this "eating junk food makes you a bad person" crap. Seriously? Uhh, if you truly feel that way, I think you need to seriously re-evalutate your perspective both on life and how you view others. If you don't want to drink, eat candy, or drink soda, that's fine. No one is forcing you to. People who do do the above things aren't bad people just because they choose to live their lives differently than you though. How would you like it if they all looked down on you for running? Seems rather hypocritical and narrow-minded. A little alcohol is actually likely to be GOOD for health anyway. A little sugar never hurt anyone either (except diabetics, haha).
I can relate to you somewhat though. I used to be pretty uptight as well. Not nearly to your extent, but I was. I still rarely drink, I don't drink soda, don't eat fast food, etc. I eat candy and icecream though, the former every day. I'll run under 4:10 and 8:15 (mile and 3000m) this indoor season unless I get injured, possibly getting close to 4:00 and 8:00. I'll graduate in May with three bachelor's degrees. I pretty much wasted my first two years of college because of a bad attitude and outlook like yours, but since then I've had girlfriends, one-night stands, gone to parties, gone on road trips, watched movies and gone out to dinner with friends, etc etc etc, and my life has been better because of it. I've also had weekend nights where I sat alone in my room and watched documentaries or read books too, and I'm not ashamed about it at all; it's who I am, and learning is something I like to do.
You need to realize several things. 1) As I said before, "normal" people aren't bad people just because they enjoy drinking et al. To me, doing nothing with your life BUT drinking is a waste of time, but it apparently isn't to them. How they choose to live their life shouldn't bother you so much. 2) Not everyone fits your mold of party-loser. There are a lot of people out there with similar (though probably less extreme) views to yours. You just have to keep an open mind and try to be more friendly and get involved in things. Do the things you love (which should include more than just running), and you will probably find people with common interests along the way. 4) There is WAY more to life than running. This is coming from somone who would like to make the Olympic trials and run semi-professionally for a while. I love running, it's a part of my life and always will be, but I love science, politics, movies, skateboarding, hiking, camping, art, traveling, and especially chasing women (not in the derrogatory sense, I just like flirting and being with women). Don't let any one thing rule your life. This might sound stupid, but you should watch "Yes Man." You might not realize all the things you enjoy until you actually start doing different things. I know that sometimes it's hard to find the time with a busy running and school schedule, but you should try and find the time, and don't pass up opportunities when they arise.
Anyway, I think a lot of people have given good advice, so I don't need to say much more. I would STRONGLY recommend you don't listen to people like candela though. You'll end up being a complete fun-killer living a painfully boring life who no one wants to be around. At your age you're still growing and changing a lot as a person and will continue to do so over the next 5-10 years. My advice isn't to change who you are; it's to discover who you are. Right now you're alive but not living. Try to start making small steps such as interacting with more people, even if it's making small talk with a cashier at a gas station while you pay for whatever it is you're buying. You'll learn a lot about people and how to talk with them just from things like that after a while.
Good luck.