Would it be morally wrong to tell a girl her man is cheating on her, just to better your chances?

Yes I know it sounds cynical, but there is this girl I’m madly in love with, and she is dating this guy who is a complete douche. He is actually cheating on her, and I’ve seen it.

Is it wrong I only want to tell her because I want her, and think if she knows he isn’t the great guy she thinks he is, that it increases my chance?

Would it be morally wrong to tell a girl her man is cheating on her, just to better your chances?
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