Facebook is a great tool for connecting people, yet it is also a tool that is inadvertently used to make people feel alone and unwanted. I don't know what can make a a guy feel more unwanted than during intramurals to see the people he asked if they wanted to make a team to say no and turn around and ask a others a few weeks later. It may not be intended to be a backstab, but since facebook has made things very open, it isn't hard to discover when this happens.
It isn't so bad when it's just a couple of people who do it, but when that number grows exponentially to where there are no "friends" left. How else can you feel? Someone might say, "you must have done something to cause them to not like you." However, how can that be when no one tells you that or even indicates that is the case. I don't know where else you can have 500 "friends" and yet feel so alone unless you are a politician.
Of course, facebook isn't the root problem. The problem is with how our society works. Facebook only makes it easier to notice, but it's our society that causes the problem. Is there a way we can fix it? Not really, but maybe we can make it so that these cases become smaller. Maybe we should do what we wish employers do. It can begin with a simple task of when you are looking for a team, ask the person who asked you earlier, especially if you consider him or her a friend.