Wong Kar Wai has observed that critics tend to read the title of this movie ironically, but that for him there is no irony. No irony in the title, perhaps, but Happy Together is deeply concerned with the fundamental irony that mercy all too often can tip over into its opposite. When Ho Po-wing (Leslie Cheung) is beaten, his estranged lover Lai Yiu-fai (Tony Leung Chiu Wai) nurses him back to health, bathing him, letting him sleep on the bed, feeding him. These acts of mercy are, at first, disinterested; the two men are no longer lovers, and Lai Yiu-fai has no desire to rekindle the relationship. However, Lai Yiu-fai becomes deeply embroiled in the relationship and mercy and selfishness begin to blend into each other. In spite of this irony, the two men find mercy in precisely the fleeting moments of happiness referred to in the title.
—Nathanael T. Booth