Everything is fair in love is not a good idea, viewed from a point of a good man. To be a good man, we need to do good things - only fair things
All is fair when love is war
well it depends. using this theory you will probably "win the battle but lose the war..." love is love.
This is a proverb by an anonymous source.
You'll find something in Aesop's Fables Try www.pacificnet.net/~johnr/aesop/ home.freeuk.net/elloughton13/aesop.htm