All I really know with any certainty is I'm with someone who makes me feel happy and good about myself... their effect on me is positive... my life is much better for it... and they feel the same effects too. Out of this I am satisfied emotionally, mentally, and physically/sexually. On the flip-side... I want to make them feel happy and good about themselves too... I want to please them emotionally, mentally, and physically/sexually...
We get along well, grow used to one anothers company... and genuinely care about each other, as well as want to listen to what the other has to say...
Call it a mere bio-chemical result.. biology... or some mythical unknown... but the simple facts are this... nobody really knows with absolute certainty how this occurs... or else we'd all be in agreement about the definitions and the causes.
Maybe it's good to have some mysteries in life... it seems to kill the boredom...
"The weakest soul, knowing its own weakness, and believing this truth that strength can only be developed by effort and practice, will, thus believing, at once begin to exert itself, and, adding effort to effort, patience to patience, and strength to strength, will never cease to develop, and will at last grow divinely strong."
- James Allen