I’m sure this very frustrating for you and you certainly care very deeply for your husband, which means you are not a monster. But I don’t know that you fully appreciate his situation. You say that your husband is in an extreme case of denial, and yet, he’s pursued coaches and therapists and psychiatrists. This suggests that he does want help. And sure, he forgets to do his homework, because he is ADHD. Forgetting to do your homework is the hallmark of ADHD. Lying about your homework is what ADHD people learn at school. It’s not the best adult behavior, but it is a learned response from years of being criticized for having the best homework intentions in the world, and then forgetting.
I imagine your husband feels criticized by you. It’s hard to make changes in your life and behavior when you feel criticized for things that are out of your control. You feel like you are trying to help him, but your best efforts are being ignored and undervalued. It’s hard to be in a relationship with someone who messes up on the basics of just getting through the day, and refuses all your help. But it’s also hard to be in a relationship where you feel like everything you do is wrong.
He may be able to accept your help with his ADHD symptoms eventually, but right now you need to repair the damage to your relationship. The damage is not your fault, and it’s not his fault– it’s situational. You can blame his ADHD for the damage to your relationship, but that would be like blaming cancer. It’s out of his control. It’s also out of yours. Even if he followed all therapeutic advice, and followed his drug regime, there would still be moments where his ADHD would rear it’s ugly head.
What you both need is a safe way for each of you to express your frustrations and concerns. You both need to be understood and heard. Couples therapy would do you both a world of good.