And how many loves have perished because, from pride, or spite, or diffidence, or that unmanly shame which withholds a man from daring to betray emotion, a lover, at the critical point of the relation, has but hung his head and held his tongue?

Robert Louis Stevenson (1850–1894) Scottish essayist, novelist, poet
Essay (1879-05), “The Truth of Intercourse,” Cornhill Magazine, Vol. 39
    (Source)

Collected as "Virginibus Puerisque, Part 4" in Virginibus Puerisque and Other Papers, ch. 1 (1881).