A bottomless pit

I am having a hard time "channeling" my frustration and fears. My husband has untreated ADHD. Since I have found this site I read a lot about ADHD, I feel informed but not helped. During our last fight I compaired my husband to a bottomless pit. The last couple of months, every night, he talked about wanting to go on holiday this summer. When I finally booked the trip I thought that would be the end of his repetitive dialogue about him needing a holiday. It lasted one night. The next day he started obsessing about NEXT year's vacation. We haven't been on this one yet let alone think about the one next year! Same thing with our car. Months and months he talked about wanting to get a new car...everynight the same speech. Finally last month we got our new car. I was relieved and looking forward to not hearing about us needing a new car everynight anymore but as soon as that thought entered my mind he started about 'his life long dream': getting a sportscar. OMG, it just doesn't stop. He's like that with everything. It's a thing he does, he sets a goal and until he doesn't accomplish that goal he is not happy. When he finally does he still feels empty and sets a new one. I think he's tries to justify this 'empty feeling' he carries by comforting himself with the thought that until he doesn't get what he thinks he needs he can't of course be happy.
I told him to live in the moment and not in the future but it's useless.
Is there something I can do to stop these daily conversational routines....i really can't stand them anymore.