You can not help him kick this habit. I realize your intentions are good but all you will end up doing is enabling him. He, and only he alone, can decide if and when he wants help.
As you've found, he'll promise you the moon and never deliver. He will continue to steal from you and call you names.
Leave him. Yes, it will hurt but it is for your own benefit. If, after you've gone he realizes that he misses you then he can complete rehab before you take him back. ONLY if he completes, not just says he will or starts, but COMPLETES should you take him back.
Lots of people have sexual problems from meth. Many find sex while not on meth to be "boring."