Nick is having inner conflicts here.
He is used to his Navy ways of getting what he wants. For guys like him, it is the thrill of the hunt and conquer. Sex has always been about Lust.
Here he does Lust after Jeremy, but he knows there is something more. He doesn't want to hurt him, both physically nor emotionally.
This inner voice we hear is his old ways of bedding down Tricks. His raw desire is urging him to pillage and plunder. But he is trying so hard to pace himself, even using some of his old relaxing techniques on Dupree that he used to use on virgins before.
David makes good points here!
Nick might appear to be "losing his shine" but in my opinion, he is desperately horny, consumed with lust for Jeremy. He is not perfect, and although he has had way more experience than Jeremy has, he is not lacking in his own share of insecurities ..
Dupree is not the only one going through a crisis, granted, he is still in the closet and Nick is not, but they are both experiencing an intense, mutual physical attraction, along with a bunch of unanswered questions.
Dupree is aware of Nick's confession that he is falling for him, he is dealing with that .. he is also now worried that Nick might return to the Navy and leave him behind ..
Nick has a hidden fear that Dupree might "decide" to go back to living as a straight guy, afterall he went on a date with Paula .. he is also aware of the fact that Dupree has not reciprocated his feelings by also stating that he is falling in love .. he wonders if Dupree will decide that he doesn't want to see him or sleep with him any more. Like Dupree, he is under some pressure ..and all of this is going in a short space of time .. Has it been a week yet?
And another thing .. Nick sounds very experienced and "together" but he is only 22 years old .. sometimes I have to remind myself of that fact .. he is still quite young.

Time'll tell ..