Did you know that the chemical responsible for the initial rush of passionate love acts very much like an amphetamine? PEA (phenylethylalanine) is produced early on in a relationship but lasts only months to a few years. Some become addicted to PEA and move from one relationship to another in hopes of reproducing that intense feeling of love (or lust)—although it cannot be sustained over the long-term. If the relationship continues, another chemical (oxytocin) takes over and promotes feelings of love, closeness, and bonding. (Source)