Reflections on a "family"

I am starting to realize something about myself, so I'm going to try to hash it out... here... in public (somewhat). I have participated in several short-term (some longer than others) activities where, at the end of it, the participants have become very close. I, on the other hand, sit back and watch this happen as an outsider. In some cases I think, "This is ridiculous; they've just met and they act like they're leaving their best friends." But sometimes I think, "We really have been through a lot together and we should be closer than I feel." One of two things is happening: either there are a lot of shallow people out there who don't know what a deep relationship is like, or I do not allow myself to get close to people quickly. I fear it is the latter.

I think I used to feel really deeply for people I barely knew, but it never seemed like they cared much about me. In actuality, they probably never knew how I felt because I'm afraid to put my feelings on the line. I also know that I often don't take the time, energy, and emotion to "invest" in relationships. I've always been more of a one-or-two-deep-friendships kind of person rather than the several-not-so-deep-friendships kind. So, is that it? Am I just satisfied with my one-or-two friendships and don't think I need any more? If so, I would say I'm just secure and don't need to depend on sporadic relationships. But, I think I would be justifying a flaw. Instead, I believe I am keeping myself from meaningful relationships- no matter how brief they may be in the end. I don't know what to do about this, but I wish I didn't distance myself like that.