Good stuff from Yoda...
You better make sure you know those other two are committed to sticking with it.. like staying in the apartment. It will be tough if you lost half your rent. You guys need to have a signed agreement on how your are going to handle the rent. Friends is friends, but business is business.
Also, it's tough for young couples to live together. If you are home, and the girl from the other couple is home.. and the others are not.... .well.. it can get complicated. Be careful!!!! That's the fastest way you could find yourself out on your ass (without a girlfriend).
You need to know what you're getting into. Rent is one thing, but all the rest starts to add up QUICK. That $400 bucks you are talking about would only be 2 months rent (your share). You gotta eat, pay the light bill, gas, insurance, clothes, and misc. It is SO expensive to live these days. I'm not trying to talk you out of it, just know that it takes a lot of cash to get by.
Last thing.. you are growing up, pretty much grown (but I know you don't feel grown up).. If you move out on your own, and are living with this girl...All grown up like... DO NOT mess up and get her preggers. Wow.. you think you don't have money now.. have a kid! I love my children, but they are money-eating machines.
Good Luck to you greasy. I hope this helps bring you some happiness and is a good experience for you.