Love is envy (chemically).

Science Daily reveals the chemical link between passionate desire and passionate jealousy:

Previous studies have shown that the oxytocin hormone has a positive effect on positive feelings. The hormone is released in the body naturally during childbirth and when engaging in sexual relations. Participants in an experiment who inhaled the synthetic form of the hormone displayed higher levels of altruistic feelings, and it is supposed that the hormone plays an important role in the formation of relationships between people.

However, in earlier studies carried out by other investigators with rodents, it was found that the hormone is also related to higher levels of aggression

The findings show that those participants who inhaled the “hormone of love” displayed higher levels of envy when the opponent won more money and of gloating when they were ahead. Another interesting result was that as soon as the game was over, no differences between the participants were evident with regards to these sentiments.