J, It sounds like performance anxiety to me. Like he is worried that you will want the same thing the next day and he is worried he can't live up to it, so he throws out a preemptive strike and announces that "that was enough" for a while. I don't know that you can do anything about this. It might be something that he needs to struggle through on his own. However, I do agree with you that it would be nice if the announcements stopped! You could use humor (that always works for me in those situations); you could say something like "What makes you say that?" and see if he will talk about his thoughts; or you could beat him to the punch and say it yourself: "Boy that wore me out! No more for us til this weekend!" I have used all of these myself and have had equal results with them--all good.
I think that this is a distinct difference between an LD man and an LD woman--the confidence issue. I can see why all LD partners have shaky confidence but the men have to deal with actual physical performance as well. Also they are socialized from an early age to expect that their woman will never be able to keep up with them--what a blow to hear, Come on you big dud where's my lovin?!
So keep on doing what you're doing--being supportive and loving and firm..he'll get there!