Why is my birthday so hard for him to remember?

Tomorrow is my birthday. For the 14 years we have been married , my DH has been consistently inconsistent about remembering it, much less planning anything, however small to celebrate. I'm not talking big, I'm talking a card that wasn't bought the morning of my birthday when he sees my face and realizes I am upset because he has, once again, forgotten . We have a 10 year old child who is learning from his Dad how to celebrate birthdays  . He has adhd also but he gets upset with himself when he realizes he didn't do anything to celebrate. How do you tell a 10 year old boy who worships his dad that he has been doing this since before you were born? I simply told him it was not his responsibility, as a 10 year old, to plan for my birthday. I said it as kindly as possible, because I know better than to bad mouth his dad- it simply is wrong to do that to a child. I spoke to my DH privately and told him he needed to talk to our son and tell him it is not his(our sons) responsibility to plan something for me.he apologized, as he always does, and spoke to our little guy. Why does he continue to do this, year after year. He did the same thing for Mother's Day. I asked him once about this when we were in therapy and he said it was "to much pressure" to choose the right gift and so he just would forget.   That was his way of coping.  This man does not deny he has adhd. He is on meds, although he acknowledges they are not working. He has done nothing to change his meds . Takes too much work. We took Melissa's course. At least I did- he couldn't make it home from work by 8:30 so many times that I don't know if he even finished listening to the sessions after they were recorded. I took a suggestion from one poster here to go to alanon meetings- it has been a lifesaver. I stay because of my child, who is a handful. I don't know if this is the right thing to do or not- I am just so sad, lost & confused. I try to pretend days like my birthday don't exist. I deserve much better treatment than this, but does my need for a happy marriage trump my sons need to have his parents together? No easy answers.