Why did william Pitt the younger never marry?

Answer 1

He had never intended to, and may have been a well-closeted gay. (No proof, but plenty of signs, as seen in contemporary Cartoons and verses.)

He was, however, a highly eligible bachelor, and after a long, friendly conversation, one girl thought he had proposed to her and rushed home to tell her mother the good news.

Pitt had to write the mother a highly discreet apology for letting himself be misinterpreted in that way.