Razumihin is charming, sweet, loving, and forgiving. Responsible for much of the comic relief in the novel, he's a real people-person, and just the guy you want around if you get sick. He'll take care of everything – even if you show your appreciation by acting like you don't care. On the other hand, he has his limits.
And this is where we can see that the friendship between Raskolnikov is not purely one-sided. When Razumihin has had it up the here with the whole situation, Raskolnikov is there to stop him from going on a drinking spree. Going on the spree probably would have meant that 1) he'd hate himself in the morning (see previous drinking spree); 2) he might do something actually stupid and dangerous; and 3) he might lose Dounia (because that's the way things can easily go in these kinds of books).
Like Dounia, Razumihin is fairly steady to begin with, but grows even more so over the course of the novel. Like Raskolnikov, he has dropped out of college, but he's been making a living doing translation. He has dreams of opening a publishing house, with the capital and a business plan to boot. He's a terrible gossip, but this becomes a positive quality in terms of the situation faced by the Raskolnikov family. If it wasn't for his blabbing, how would anybody else in this book know what's going on? Plus, much of it is motivated by his desire to do good and help the people he cares about, which appears to be the family Raskolnikov.
It is this connection, this special link to these special people, that seems to provide him real satisfaction and happiness.