WOW...thanks so much for all the suggestions and resources. Also for the reminder that there are skills/techniques one can use to better manage this condition. I'm not sure our guy would see the behaviors that concern me as possibly related to ADD, but it might be worth discussing with him as he's the one who told me he has ADD. And...I don't think he thinks of himself as a particularly thoughtless and/or uncaring person. So, maybe he'd consider another possibility for his sometimes hurtful behaviors.
As for the "good" side or the "gifts" of individuals with ADD.....I would agree. That's part of what keeps me hanging in there instead of walking away.
I do, however, think that certain aspects of poly relationships further complicate some of the challenges of having such a condition.