In Chapter 9, Holden informs the reader that "last year I made a rule that I was going to quit horsing around with girls that, deep down, gave me a pain in the ass." He goes on to admit, however, that he broke his rule the very day that he made it with a "phony" girl.
Although Holden believes that "in his mind" he is "the biggest sex maniac you ever saw," he actually does think that sex should be reserved for people in relationships. He believes that "if you don't really like a girl" you should not "horse around" with her. Obviously, Holden's actions don't always support his beliefs.