"Misery loves company." She may not be an addict but she gets something from keeping her son coming back and charging him and I highly doubt it is to make him accountable. I will never understand how anyone could do something that hurts their own child but there are some very sick people out there. Yak is right though and at the end of the day it is your husband who makes the choice to buy and use drugs. What have you said to him about this and has he ever talked about getting help?
Have you told your MIL exactly what you think of her selling drugs to her own son? I would have a very difficult time having any sort of relationship with someone who would lie to me and do that behind my back. I am so sorry you are going through this but glad to see you attend meetings. Glad you found us. Vent all you want. It is what we are here for!