Am I being oversensitive about my friends?

[TennisDude]

I usually hang out with my little group, mainly 4 people. One of them is my best friend and he's called me his best friend before too. But lately I've been really paranoid on whether he really meant it because he usually spends most of his time with his other friends and not me, and we usually only talk online or in, say, one class of the school day.
I don't know why having a "best friend" is so important to me, but it is, for some reason. Really, it's all I want. Whenever I'm with friends I usually feel like I'm just kind of there and not really wanted.
But I have a lot of great friends. I've just never felt like anyone ever liked me more than their other friends, and for one reason or another that's what matters most to me.
So really,
-Am I being too paranoid about this?
-Is having a best friend really so important when I have other friends?