Final answer:
Doug and Danni's long-term relationship exemplifies companionate love, which includes intimacy and commitment but not passion, while Marcy and Martin's recent and passionate relationship is an example of infatuated love.
Step-by-step explanation:
Doug and Danni are experiencing a stable and mature form of love, which is known as companionate love. This type of love is characterized by deep affection, emotional closeness, and commitment, but it does not necessarily include the passionate aspect of love. On the other hand, Marcy and Martin, who have only been together for a short period, are likely experiencing infatuated love, which is marked by a strong, often overwhelming desire and passion for one another without the established intimacy or long-term commitment that defines companionate love.
According to Sternberg's triangular theory of love, companionate love is made up of intimacy and commitment but lacks passion. In contrast, infatuated love possesses passion in the absence of the other components. Therefore, Doug and Danni are experiencing companionate love, while Marcy and Martin are experiencing infatuated love.