How dangerous is an open heart?

Something happened to me today made me to think about what 'friendship' really is? It is easy to meet somebody, be someone's friend and have fun with the person. But, it seems hard to maintain friendship when something come up and you and your friend can't see the thing the same way. Or is it because of me? Sometimes I got betrayed, sometimes I ditch others (I never betray my friends, but I ditch some because the communication didn't work) But I think, that is something about making friends, right? Friends come and go, it is ok, because you will always meet someone new in the future, in different periods of time due to different reasons, out of different interests you share. Of course, I have a few close friends that I know for a long long time, but not so many though. Why should I care so much? Why can't I care less? Yes...because we are human not animals, of course~~~