Re: ADHD FiancÚ is Extremely Frustrating!
Unfortunately, I don't think there's much you can force here. From what I've seen in your post, your boyfriend suffers from the 'primarily inattentive' subset of ADHD. He needs treatment if he's going to have a chance at being the focused and successful person you're hoping he'll be. If not, he's going to continue dreaming big dreams without following through on anything.
All I can offer in the way of ideas is something along the lines of this: He needs medication. On the plus side, I can guarantee that the meds will make him feel differently than they did when he was a kid. Children react to medications in different ways than do adults, and while stimulants tend to make kids feel like zombies, they make adults feel more awake and aware. While children complain that stimulants leave them in a fog, adults tend to describe the experience as a fog being lifted. That's not to say that he will definitely be free of side effects, and finding the right med that offers the right combination of effects vs. side effects can be a long and frustrating process. Again, he needs to be convinced of the fact that ADHD is holding him back, and he needs to want treatment.
This is the process as I would recommend it:
1. Find a psychiatrist that specializes in adults with ADHD.
2. Find the right med or combination of meds that give him the most benefits with the least side effects.
3. Get a referral from the shrink for a psychologist or ADHD coach that can lead your boyfriend through Cognitive Behavioural Therapy (CBT).
Seeing as you're from the US, all of this will likely cost a significant amount of money. If there's no option for really good health insurance, you could try sending him to a general practitioner and get Adderall (Vyvanse is probably better, but Adderall is generic in the US now), and try to get the treatment by doing your own research. Go pick up a book called You Mean I'm Not Lazy, Stupid or Crazy?! by Kelly and Ramundo, this will be a good jumping off point in your search for information and possible routes to treatment.
Best of luck.