Blushing is thought to be linked to increased levels of norepinephrine in the brain, which may be associated with romantic feelings. It signals that we are interested and excited, which is attractive to men.

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

When you massage someone, the levels of oxytocin go up in the brain, and oxytocin is one of the chemicals that drives attachment.

Romantic love is an addiction.

Women are very attracted to a low voice because it's linked to testosterone, which for millions of years was a sign that men had very good spacial skills and would have been very good at hunting and finding their way back home.

The human brain is built to compare; it's Darwinian to consider an alternative when one presents itself.