I have been through this with my Son who has been drug free going on 5 years.
It was a long hard road that I hope and pray he is never on again.
Meth is a nasty addiction that steals your whole life away from you. I wish him the best and he is lucky to have someone like you in his life.
My DIL went through pure hell with him. The mood swings are so nasty,which I'm sure you probably have experienced.
My Son actually ended up in prison due to his using and it almost killed me,it was the most heartbreaking thing I have ever endured.I actually think worse than losing my Parents.
You feel so hopeless. They really have to want it to succeed.
Please don't ever be his enabler in this,stay strong. I will keep you and your family in my prayers.