You don't mention his current state. That makes a huge difference. I was diagnosed with mci with diffuse lewy bodies 3 years ago when I did tests because I thought something wasn't right. My neurologist said he doesn't usually sees some this early.
My wife freaked out, assuming I would be a burden within just a couple of years, should stop driving and attributed anything and everything to my decline even when there's another explanation, like lack of sleep, lifelong ADHD, or long-term depression to name a few. I spent the next 15 months having my driving tested (it's fine), learning about dementia, trying to justify my existence. Finally, after the 3rd doctor visit together and hearing again that mci is different from dementia, and my timetable is unknown, she backed off. I still have to point out not everything implies dementia. I still easily handle the 10 areas of independent daily living.
My memory isn't quite as good, especially misplacing my car keys; my sleep a little more off, but improving; my ADHD symptoms are more obvious; my eating is less regular; I get less done in a typical day. I still manage medical care, which includes making sure my 7 primary professionals are on the same page and we are all going in the same direction.
I suggest: live in the moment and set times to think about the bigger picture; create some good times, get a good professional resource and use them (doctor, geriatritian, counselor, social worker, speech and language therapist- they're trained to identify coping mechanisms - I've used all of these for different pieces); treat him with respect (includes letting him do for himself what he can); use his phone as a memory aid with calendar for appointments, including destination to use with map app, contacts, photos, etc.; don't assume a new issue can't changed, while not everything can; help him stay physically and socially active.
Most importantly, learned from having a daughter with Down Syndrome, take care of yourself first. I doubt you are still 30, and you can't help much if you're very frazzled. Treat yourself with respect and take care of yourself as well.
I'm open to private messages.