Hey there, so sorry to hear about you and your friend. I can't offer much advice on this, but since you're asking for insight as an addict I'll go out on a limb...
Most drugs trigger the reward centres of your brain. Strong drugs can make you feel better than you ever thought it was possible to feel. The downside is that when you're off them, you carry on wanting that high. And now your brain knows how good things CAN be, everything else pales by comparison. Yes, even all those years of friendship.
I'm really sorry, but in the face of a drug like crack, it's really unlikely that your friend is going to listen to words of reason. My heart goes out to you both. Remind him of who he is, be there when he crashes and is ready to clean up, and don't give him any money. Give him the website for this forum if you like - reading it might shake him up a bit.
But do not, do not blame yourself in any way. And stick around here - you're very very welcome, all of the time.
Sorry I couldn't offer anything more concrete.
Still
xx