Hey S, it really is difficult watching someone we thought we knew become someone we don't recognize. That's why I am convinced that they are in crisis. Does that excuse them having an affair? Absolutely not!
Your h is a teenager right now. He doesnt want responsibilities or pressure. Try not to get into those discussions with him. He is not hearing you. Take what he says with a grain of salt.
I know how hard it is for you to see your children hurt. That's why you have to concentrate of them and on yourself. You will have to be the one who gets them through.