Love can be ambiguous. Just ask any group of people how they would define it and you are sure to get a swathe of answers. Robert Sternberg decided to create a classification system to objectify love in 19886 and it's still widely accepted as accurate. Intimacy, Passion and Commitment are the three main categories, with combinations of the attributes describing particular relationships. Intimacy is closeness, passion is sexual drive and stimulation and commitment is the glue for a lasting love.
These types of relationship titles are determined by the strength of the components being combined. For example, each taken in isolation; if you "like" someone then you mere have intimacy out of the three. Empty love would be commitment, with passion or intimacy, such as an arranged marriage. Love with only passion is nicknamed infatuation. It is basically a formula, with a combination example being "romantic love," or the presence of both intimacy and passion but no commitment. The idealistic, life-long variety of love can only be felt with all three bases fulfilled.
In 2002, a psychologist named Wojciszke came up with the idea that each of these stages usually forms in the course of a relationship. There's a progression through the tiers up till consumate love. First, it starts with passion, then there's romance, which is passion and intimacy. Feelings become solidified when there's a commitment from both parties, completing all 3 categories. Long-term relationships can sap a couple of their passion though, still committed, reverting them into a form of companionate love. A south bound relationship usually is only held together by commitment, until they break up, leading to dissolution where they fulfill none of the categories.