There is a quest (I think it's called don't tread on the bear) that serves as an indicator of your progress with the NCR ending. If you get the quest, you are close to ruining it. If you fail the quest, you have progressed too far to finish with the NCR ending. You can check your quest log for that. As long as you are not hated to the point of being shot on sight, you can still keep doing NCR quests for fame. I think just doing their ending and nothing more is enough to get you to idolized if you earn no infamy.

He will give you the next quest in the chain. Things That Go Boom. The NCR, like the other New Vegas factions, wants the Boomers on their side. Guide on how to play dfo on parallels for mac.