Norman Doidge

In Elizabethan times lovers were so enamored of each other’s body odors that it was common for a woman to keep a peeled apple in her armpit until it had absorbed her sweat and smell. She would give this “love apple” to her lover to sniff at in her absence.

we have two separate pleasure systems in our brains, one that has to do with exciting pleasure and one with satisfying pleasure. The exciting system relates to the “appetitive” pleasure that we get imagining something we desire, such as sex or a good meal. Its neurochemistry is largely dopamine-related, and it raises our tension level.
The second pleasure system has to do with the satisfaction, or consummatory pleasure, that attends actually having sex or having that meal, a calming, fulfilling pleasure. Its neurochemistry is based on the release of endorphins, which are related to opiates and give a peaceful, euphoric bliss.

We love being in love not only because it makes it easy for us to be happy but also because it makes it harder for us to be unhappy.