I suspect he's saying it's impossible for someone to still be horny after getting their rocks off once, and that he doesn't like that the sister hooks up with anybody other than the brother.
I can speak from personal experience that it's possible to get my rocks off more than once in a single day, heck even in a single sex session, and it definitely goes for women as well from my experience with my wife and some other girls from before I got married. Hell, when I was Taylor's age I could get my rocks off 4 or 5 times a day easy, and even now while I'm in my 40's 2 times is easy, and 3 times is achievable (but not too often if I want to live :closedtongue
.
As for the story, I actually like the sexual tension that's building between Taylor and Nikki, and the fact that they're not just jumping each other right of the bat. Nikki's liberal approach to sex and her helping Taylor is great, and I'm hoping that Taylor gets to help her sort out the situation with Grant the douche, or better yet, unleash Ashley on Grant.