what am I good for?

Yesterday I hurt the person I care for most in this world (apart from my parents). I still don't know how I did it, but it seems that I did something wrong.  her status message said that she is hurt. I was terified, I thought she had an accident or something. I can honestly say that I probably had never been so scared in my life (my adult life anyway). 

I frantically SMSed and called her but she didn't reply. Finally at around midnight, one of her friends contacted back saying healthwise and everything ashe is fine, he had met her a couple of hours ago. So that brings me to the point that if she is not not hurt physically, then it must be mentally and since she isn't talking to me then it must be my fault.  

That brings me to the question about what exactly I am good for.  I know I am not a good son or a good grandson. I sure as hell am not a good employee, never was a good student. One thing I had was the feeling that whatever else I suck at, at least I am a good friend. 

But a friend, a true friend is not supposed to  hurt the person who is closest to him is he? And yet here I am doing precisely that.  I treated her badly for something silly, I was not there for her when she needed me as a friend and then I pretty much screwed her happiness and peace of mind before her wedding by selfishly proclaiming my love just before her marriage.  And now this?

I mean has there ever been a worse friend in the annals of friendship?

which again brings me back to the orihginal question, sicne I am not even fit to be a friend, so what exactly am I here for? What's my purpose?

What am I good for? What??