Thy shalt not crumble

Ok, for all my resolve to not be forgiving, i must admit its very hard for me to remain angry for long. I need to keep intoning my new mantra "Thy shalt not crumble".
Yesterday he attempted to message me twice. I saw his name blinking in my Yahoo IM and a cheery "hello!" pop-up came on.
I shut the pop-up but felt guilty. Another attempt came on at 2am with "Can't sleep?". I switched off laptop and went to sleep, again wondering if I'm being unreasonable. But the other part of me argues that he's an asshole and assholes dont have friends. One day i will probably explain to him why we can't stay friends anymore. If he's still interested to know that is. But how do I even start to explain to an ex-friend that I really cannot stand him anymore. That his very character which I loved once is now anathema and everything that now comes out from his mouth appalls and sickens me. How scary it is that a person can change so much with time. Or maybe it's been there all along but i'm too blind to notice as usual?