Emily,

Correct me if I am wrong.

Your H left for OW

You H smokes pot and pop diet pills and ritalin (which is actually speed. it makes hyper kids calm down b/c their brains work opposite to chemicals)

You have some anger. You are mad at your hubby and your past (mom)

Your daughter's health concerns you....as it should.

My suggestion, assuming I have read your situation correctly, take care of yourself and your child.

Kevin is filling his void with pills and the OW. Until he quits those he will not realize that you and your marriage can fill that void.

You cannot make this decision for him.

You have other demons and battles to face.

Concentrate on your daughter and yourself. NOT your mom NOT kevin. NOT the OW.

You have some healing to do, and maybe by putting your efforts towards your daughter and yourself you will get there.

I may be off base. Just my gut reaction. Take it with a grain of salt.