@Author
There are many answers and debatable offerings which you can read. What is important is who wants to break up? If it is a girl then the feminists (most loud) would says she must have a genuine reason to that however if it is a boy then it is breach. Moreover if after s*x a boy leaves the girl then it might amount to even rape but for a girl it's genuine excuse/reason.
Choose your fate! A girl would have s*x only with that guy whom she herself likes too much and whom she doesnt want to loose ever because she believes that this is the guy who can make her upcoming life brighter. But if you try to steal this dream away, she won't wait a second to call you a criminal. However converse does not follow and legally excused !!
Follow my upcoming post on Are girls really backward?
//peace
/Saurabh..V