I love you for her means that you care about someone only because of a third person, and there are I love you for her quotes out there that show the insensitivity of this phrase. Sometimes a guy will pay attention to a female who is not their main interest in the hopes of getting closer to their true target, and sometimes they may start to care about someone just because the female they love more than anything also cares about the individual. This emotion is not true love, even if you are fond of the person. If it was not for the sake of the third party you would not care the same way. This can be a shallow way of thinking and any relationship will usually be short lived.