I ain't trying to scare you, but if you live a statistically average life you're about to hit a downward trend in your mood which will last a couple of decades. By the time you're thirty you'll likely have a boss, a spouse and kids, all of whose needs will have to come before yours. Things start to improve again at age 47 when the kids have moved out and you're at the top of your career.
Maintain your friendships. It's so easy to make them a low priority, but having good friends and being a good friend to them is the way to make it through.