Rejection Sensitivity Disorder and ADHD

My husband has been diagnosed with ADHD, is 60 & agrees he may have it, but will not medicate.  Our marriage of 28yrs has always been a struggle due to his ADHD.  Last year he betrayed me by cheating on me online.  I was devastated  and did not understand his behavior at all.  It was way out of character for him.  We have been going thru counseling and he said he felt I did not love him any longer.  I know at the time I was requesting more of him in the relationship and he felt rejected.  I recently have been reading about RSD and ADHD.  I now know my husband was experiencing the effects of this disorder and that is why he cheated.  However, I do not feel I can approach him about this because whenever I try and talk about the ADHD he says I am just trying to find things wrong with him.  I am attending Al-anon and trying to stay in my lane.  How do I have a relationship with someone who is so sensitive?