Hey FeliciaM!
I'm glad you're here. Your situation is exactly why the AA BigBook calls this a "cunning and baffling disease."
I don't know why they all get like this. I am wondering if the substance disables parts of their brains that control feelings and relationships.
If you get that TV show "Intervention" you might want to watch it sometimes. The alcoholics on there are every bit as bad as the CrystalMeth users.