Weighing up

Just now I was contemplating two friends and wondering which one I was closer to. At first, I thought it was easy and knew for sure which I was closer to. But at second glance I began to think more closely. One of them I've "trusted" (in the simplest sense) more and opened up to more, however the other I talk to more and see more often and we are quite close. I can't really decide anymore. What defines closeness? Some people I'm close to because we see eachother everyday at school (and they're in my classes and what not), others because even if I didn't see them for an entire half year and it still wouldn't be the slightest bit awkward ringing them and chatting for hours and we'd still be as close as always. And sometimes I think the only reason I am close with the people I see everyday is simply because I see them everyday, which is logical enough in itself. But I think that with some of them, if I didn't see them for ages I wouldn't just be able to ring up and have a full on d'n'm with. And to think that the closest type of closeness is based on mutal trust would be silly, wouldn't it? I'm not exactly consistent in my reasons why I trust people and open up to them, there's a lot of peripheral thought that comes into it. So yes, now I'm confused, but that's enough thinking for today :)