Remember the "women's pictures" of the 30s and 40s, often starring Joan Crawford, Bette Davis, Barbara Stanwyck? A powerful identification element for members of the female audience aspiring to love, wealth, status, even if the leading lady, now fallen or abandoned, is left wondering whether she might have been better off before her quest.
What does this have to do with "The Heatbreak Kid"? Everything! Here is a "men's picture" for our times, even though it is now nearly thirty years old. Happiness is the next woman you meet, because the one you have is not what you imagined her to be. She never will be. If Lenny, married to Lila for three days, decides he has made a mistake, the appropriate downbeat ending of this picture suggests that, on the day of his wedding to Kelly, he has reached the same conclusion.
Sometimes happiness lies in being satisfied with less than the ideal. That's what you're going to end up with anyway.