Was Washington Irving gay?

Richard Brookhiser examines a new biography of the writer:

[H]e was a restless man. He traveled constantly, never married and did not buy a home of his own until his 50s. "His smile is one of the sweetest I know," wrote a woman friend, "but he can look very, very sad." Was he gay? [Andrew] Burstein examines the question without prurience or presentism and concludes that he doesn't quite know. There are no deeply intimate relationships between men and women in Irving's fiction; what he lost in realism, though, he made up in myth.

The book is called "The Original Knickerbocker." From the Publisher's Weekly blurb at that Amazon link:

... Burstein thinks it more likely the writer was simply a bachelor, a respectable role in his time and place.

What do you think of this practice of examining external facts of the life of a person long dead in an effort to determine his sexual orientation? Are we engaging in "presentism" and failing to understand what was done in other times and places if we assume that unmarried men who have no apparent intimate relationships with women had a homosexual orientation (whether acted upon or not)?