Cheswick is one of the Acutes, the first patient to support McMurphy when he pits himself against Nurse Ratched. When McMurphy doesn't support Cheswick in his own stand against Nurse Ratched, Cheswick commits suicide.

What part does Cheswick kill himself?

Ratched sends Cheswick to Disturbed for a while. After he returns, on the way to the pool, Cheswick tells McMurphy that he understands why McMurphy no longer rebels against Ratched. That day, Cheswick's fingers get stuck in the pool's drain and he drowns in what is possibly a suicide.

Does Cheswick kill himself in the movie?

The film employs the initial altercation between McMurphy and Washington as the impetus for Nurse Ratched to send McMurphy, Chief, and Charlie Cheswick (who doesn't commit suicide in the film) to the Disturbed Ward. Perhaps the most telling difference between the film and the novel is the ending.