I'm certainly not giving medical advice, but 4mg/day is quite a low dose for maintenance. If he is still craving drugs, he could be needing a larger dose. A properly-maintained patient should not be experiencing withdrawals and cravings. I have known patients who try to keep their dosage low in the hope that they can use. If he is not honest with his doc, problems are sure to follow.
Janie, you sure appear to be giving your best efforts to helping him. Please don't neglect yourself! Just because he uses and has problems does not mean you aren't doing all you can. Programs like Al-Anon and Nar-Anon are specifically for those close to an addict. Getting together with people who are living through what you are (or have done it) can provide you with the support YOU need.