Why is Holden thinking of joining a monastery?

Holden worries that Stradlater had sex with Jane during their date, because he knew that Stradlater was capable of seducing girls quickly. Holden asks Ackley whether or not one has to be Catholic to join a monastery.

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Holden follows his thoughts on Jane Gallagher by musing about joining a monastery and thus becoming celibate. Holden seems to harbor a disgust for any type of sexuality, whether Ackley's obviously false boasts or Stradlater's successful seductions. At this point Salinger leaves ambiguous the actual reason why Holden would be concerned about Jane Gallagher in particular, for the only information Holden gives about Jane is that they would often play checkers together.