I think romantic love evolved to enable you to focus your mating energy on just one individual at a time, thereby conserving mating time and energy.

Romantic love allows you to focus mating energy. Attachment sustains that relationship as long as necessary to raise your baby.

The brain system for romantic love is associated with intense energy, focused energy, obsessive things - a host of characteristics that you can feel not just toward a mating sweetheart, ... there's every reason to think that girls can fall in love with other girls without feeling sexual towards them, without the intention to marry them.

Romantic love is an addiction.

The reason you take antidepressants is to feel calm. And romantic love is not calm - it's elation, it's mood swings, and you're killing all that when you take the drug.

Any kind of novelty or excitement drives up dopamine in the brain, and dopamine is associated with romantic love.