People (should) like each other for who the person really is. Not for what they do. You becoming a vegan would make you fake in a way. You're doing it for the wrong reason - to impress someone else. That decision would screw you over. Even if she got with you, your becoming a vegan wouldn't have an impact on it, and it would deteriorate things because you acted a certain way to impress her.

If you have to become a vegan to get her to go out with you, she isn't worth going out with.

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If a dream comes true... then is it still a dream?