what will you do if you and ur sister fell in love w/the same guy?

I have a question, which one of the sisters does the guy love? It doesn't matter if both of you love the guy, what matters is which one he prefers. If he loves one of the two sisters, then the other should understand and give way to that love. But if the other sister (the one the guy doesn't love) does not understand and does not sacrifice her feelings to make two people close to her happy, then, that would be a problem. If I am in love with a guy who loves my sister, I would try very hard to forget my feelings to that guy coz it will get me nowhere and it would only bring pain if I persisted on what I was feeling. Plus, if he will make my sister happy, then I would be happy to step back. That's how a good sister should act.