Stages of a relationship with the opposite sex:
1) Lust (Infatuation): This is what we call 'love at first sight', which is in fact, lust. Lust is when a person is attracted to a member of the opposite sex based on physical appearance and perceived notions of his or her personality.
2) Love (Romantic Attraction): The second stage is love. This is when a couple begins to delve deeper into each other's personalities and are not attracted to each other solely on lust. They are now attracted to both physical appearance and personality on an equal level, and it is in this stage that a couple begins to grow a strong emotional bond for each other.
3) Sex (Reproduction and Sexual Pleasure): The third stage is sex. When a couple has formed an intense emotional bond for each other, they will now desire to form a new kind of bond, a physical bond with each other through the union of bodies known as sexual intercourse. This is the stage when a couple becomes comfortable with each other (mostly) physically, as opposed to love, when a couple becomes comfortable with each other (mostly) emotionally.