How to bring up ADHD with my love

I have been seeing a wonderful man for nearly 2 years. He is 35; I'm much older. I love him very much and (as much as anyone can know another's heart and mind) truly believe the feeling is mutual. I have seen many signs that point to adult ADHD and these have accumulated to the point where I feel I need to bring up the topic of ADHD with him and ask whether he thinks this may be the cause of some of our relationship issues and his life challenges generally. Examples: Failing to follow through -- hardly ever calls when he says he will, couldn't get the paperwork together for a project I tried to help him with several times, broken promises (for example, he offered to sell me an unneeded family car and fix it up for me; after 3 months of delays -- needed more fixes, 2 lost titles, etc. etc. etc. -- I found another car on my own but several months later he has not paid me back a cent of the money I gave him), shows up unannounced saying he lost another cellphone with my number in it (3 times), lies on impulse (maybe to tell me what he thinks I want to hear?), forgets simple facts like whether I have a cat (he met the 2 I did have but they died last year), pops in for short visits but never seems to have the time or inclination for a real date, always working hard but always broke, seems totally clueless to my feelings most of the time, says he feels he has let me down but doesn't change ... The good stuff: deep sexual and emotional intimacy despite all of the above, faithful, spiritually in tune with me, great sense of humor, very bright guy who's fun to talk with about nonpersonal things, talented and successful in his field.

After yet another no-show, with no explanation, for a date a couple of weeks ago, I decided it was time to bring up communication issues next time I saw him. About the broken date, I asked what happened and he said he was on call for work. I asked if he remembered we had plans and if he got my "How's your day looking? Please let me know" check-in voicemail that morning. He said yes to both. I asked why he couldn't have taken a few seconds to text or call to let me know he had to cancel. He said when he's on call "everything else goes into another compartment." He seems to have really heard me (although he was on a mission to find something and checking his phone most of the time). He repeated that he feels he has let me down and knows it must always seem like he just comes to me when he needs something. I asked if I have ever let him down and he said no, I'm always there for him. He repeated my concerns back to me: feeling demeaned by lack of common courtesy when he needs to cancel, wanting real communication instead of 1-word answers to questions about how things are going with him, wanting him to really make time for me instead of squeezing me in between appointments, etc. He told me he loves me deeply but there's always so much going on.

Since we had the talk last week, he has texted me once "just to check on you" and that was sweet. But if this relationship is to continue without frustrating both of us, I really believe I need to mention the possibility of adult ADHD and perhaps share a self-assessment with him so he can decide if this is where many of his life challenges are coming from. Can anyone suggest a loving, nonconfrontational way to do this? I don't want to present it as something that's wrong with him, just that maybe he has different brain chemistry that leads him to organize thoughts and process information differently than most people. Thanks in advance to anyone who can help!