Taking Advantage

I don't like it when some people are just taking advantage of me. They only look for me when they need me. But when it's my turn to do that, it's as if these people vanished into thin air. I sent them a text message, ym or even email, yet I could not reach them. And when I happen to see them by chance, they don't even give me some explanation. It's as if nothing happened. Ouch! Well, now I know what's my approach to them, too.