Quote:"There was immediate chemistry between them the first time the met.".
I think you mean "they" instead of "the". People are more willing to spend time answering your questions if you are willing to spend time writing them clearly.
In the Western World part of the concept of romantic love is that there is a deep love bond between two people. In the Age of Science the notion has developed that certain chemical secretions play a part in both love and lust.
Your author is suggesting that these lovers are drawn to each other because of their basic chemical/physical makeup.
It is a way of saying "love at first sight".