"Интересно, что Вы говорите, что влюбленность переходит в любовь и пр. В чем разница между ними? Какой ингредиент отсутствует в одной из них и присутствует в другой?" - Ну у вашего любимого Стернберга это изложено довольно четко и ясно , Влюбленность или  Infatuated love : "Infatuated love is pure passion. Romantic relationships often start out as infatuated love and become romantic love as intimacy develops over time. However, without developing intimacy or commitment, infatuated love may disappear suddenly."  Любовь или Consummate love : "Consummate love is the complete form of love, representing an ideal relationship toward which people strive. Of the seven varieties of love, consummate love is theorized to be that love associated with the “perfect couple”. According to Sternberg, such couples will continue to have great sex fifteen years or more into the relationship, they can not imagine themselves happy over the long-term with anyone else, they overcome their few difficulties gracefully, and each delight in the relationship with one other.[1] However, Sternberg cautions that maintaining a consummate love may be even harder than achieving it. He stresses the importance of translating the components of love into action. "Without expression," he warns, "even the greatest of loves can die" (1987, p. 341). Thus, consummate love may not be permanent. If passion is lost over time, it may change into companionate love. " Ну и в табличке там очень четко видно - влюбленность характеризует только страсть, любовь включает в себя все 3 составляющих.