Friends, and what do they mean for you?

I have a friend who once thanked me for him being alive, now he won't talk. That actually follows patterns of I know of him, when he is with a woman, he knows no one but her and they get tired of him and he then he needs a friend. I've been that friend, helped him from his once suicide watch, and now if I call him, dead end.. you have reached (voicemail)

Yet you know when his life blows up again, he'll be reaching for you. When do I cut the ties? I don't want to, he is a dear friend, accepting flaws I see, but somewhere it becomes he is selfish, not seeing how others have cared, once his needs are fulfilled he forgets, and if I forgive and forget, when there were times I could have used him, I'm giving him carte blanche to carry on his reckless ways.