dropping the wrong lover you've chosen....

Tweet

my friend has this problem.he loved a girl for 2 years without proposing to her.then,on the last valentines day he proposed to her and she too accepted him as her lover.things went on smoothly for the past 1 year.then,her activities began to change.many of our friends saw her drinking in a bar and kissing someother guy and informed to him.but he didn't believe it.his belief was broken last week during our college festival.when asked,she told that we were wrong and says she still love him and doesn't want to leave him.but my friend realised about her character and wants to drop her.what is the best way to do it?