Newton in a romantic mood

  Universal law
"Love can neither be created nor destroyed,it can only be transferred from one girlfriend to another with some loss of money"

  First law
"A boy in love with a girl will continue to do so unless an external agent{brother or father of girl] comes into play and breaks the boy's legs".

  Second law

"The rate of change of love of a girl is directly proportional to the bank balance of the boy and the direction of this love is same as the increase or decrease of the bank balance".

  Third law
"The force applied when proposing a girl is equal and opposite to the force the girl applies when slapping the boy".