How does Bernard use John for his own purposes?
Bernard Marx has always been something of an outcast in his society. He does not look quite right for an Alpha and so there are all these comments behind his back about what might have happened to make him the way he is. So he is somewhat of an unhappy person.
When he finds John, he is suddenly a celebrity and he uses John that way. People want to be around John and Bernard is the gatekeeper. So he sleeps with girls who want to meet John and he uses John to allow him to meet people who would usually be way too important to bother with Bernard.
Henry Foster went out of his way to be friendly; Benito Hoover made him a present of six packets of sex-hormone chewing-gum; the Assistant Predestinator came out and cadged almost abjectly for an invitation to one of Bernard's evening parties. As for the women, Bernard had only to hint at the possibility of an invitation, and he could have whichever of them he liked.
There are even more important people mentioned a little later in Chapter 11.
The Chief Bottler, the Director of Predestination, three Deputy Assistant Fertilizer-Generals, the Professor of Feelies in the College of Emotional Engineering, the Dean of the Westminster Community Singery, the Supervisor of Bokanovskification–the list of Bernard's notabilities was interminable.