He's got a wife and kids and is doing Xtal-Meth?
Bro, you're right to be concerned as a friend, but he as a family man needs to be brought back down to earth.
Do whatever it takes, lay the nastiest guilt trip on him about his drug use fucking up his kids if you need to (because you do know thats where it's heading)...
I can accept some hobo crackhead throwing away his life on dope... his life is his to do with as he wishes. Your buddy is a family man with kids, his life is NOT HIS. He shares it with his family. If he gets his ass addicted to something as nasty as xtal-meth he's going to destroy his family and rob them of "him".
*sigh*
As others have said, he'll do what he wants... but in the end the real victims will be his wife and expecially his kids.
Red