First, there is evidence that Buchanan had close relationships with other men. For example, he had a lifelong friendship with William Rufus King, who served as Vice President under Franklin Pierce. Buchanan and King lived together for many years, and they were often referred to as "the Siamese twins." In addition, there are letters from Buchanan to King that suggest that they were more than just friends. For example, in one letter, Buchanan wrote, "I can never cease to cherish the recollection of those happy hours which I have passed in your society."
Second, there is evidence that Buchanan was not interested in women. For example, he never dated or showed any romantic interest in women. In addition, he often made disparaging remarks about women. For example, he once said, "Women are like cats - they love to be petted and flattered, but they cannot be trusted."
Of course, it is also possible that Buchanan never got married because he was simply not interested in marriage. He may have been too busy with his political career to think about marriage. Alternatively, he may have simply not found the right woman.
Ultimately, the reasons why James Buchanan never got married are not entirely clear. However, the evidence suggests that he was either homosexual or simply not interested in marriage.