Only Facebook Friends

You ever have an awkward moment where you run into an old friend and realize that they don't really think of you as a friend anymore? Maybe you make a joke and they respond flatly as though they really don't care at all? You're happy to see them, but they don't seem to care one way or the other about you?
Yeah. That happens to me every now and then.

Facebook doesn't help. It keeps me in contact with people who I otherwise wouldn't see, but for all I know it's one-sided. I'm seeing other peoples' posts, but what if they have me removed from their news feed? Or what if they just don't care?
I try to make a funny comment or say hi, and often times all I get are flat responses or nothing at all. Usually (always) this happens with girls. Guys don't do this; I'm not sure why. I like to think it's because us males are less emotionally wishy-washy, but I have no idea.

There comes a point in most of my friendships with girls where I realize that we're no longer friends; we're only "Facebook friends." Acquaintances, really, who are only friends on Facebook because we met each other once. We're Facebook friends more out of politeness than anything else, and because it might be nice to know when someone is getting married or turning 21, not because we're actually supposed to communicate.

I'm not really sure why it happens. As near I can figure, it's because people move on with their lives. I don't really associate people with points in my life, exactly, but I understand that other people do. For other people, I'm part of their "high school" life or their "college freshman year" life, and have no purpose in the present. Thus all previous emotional ties are cut—from one end, at least.

It's hard not to feel a bit inadequate when this happens. Was I not good enough to keep as a friend? Not fun enough? Not sensitive enough? Not attractive enough?

It feels sort of embarrassing, too. Like I'm accidentally being rude and overemotional, when I didn't really do anything out of place. I just didn't get the memo.