Was James Buchanan the only bachelor to serve as the president of the United States?

To date, James Buchanan is indeed the only bachelor to have served as president of the United States. This has led many historians to speculate over his sexuality. Some of them have suggested that Buchanan was gay. If he was, then there was no way that he could've come out during his lifetime, as homosexuality was not just illegal in those days, but widely considered immoral.
It is believed that Buchanan may have developed some kind of romantic attachment to Senator William Rufus King of Alabama, who served as vice president to Franklin Pierce. Theirs was certainly a very close and affectionate friendship, as their voluminous correspondence testifies. Whether things between them went beyond that, we'll simply never know. What we do know is that despite his name being linked to a number of eligible young women in his youth, Buchanan remained a life-long bachelor.