The End (1978) on Netflix

Wendell "Sonny" Lawson learns that he's dying from a rare disease, he neglects mentioning this to his ex-wife, daughter, and mistress. He then decides to end it all by committing suicide. One night he takes a fatal overdose of pills and wakes up the next morning in the room of a psychiatric hospital. He then meets fellow patient Marlon Borunki and the two of them come up with ways for Sonny to kill himself, but hesitates every chance he gets. Finally, he goes to the ocean and tries to drown, but develops an epiphany and decides he doesn't want to kill himself, but apparently Marlon has other plans for him.