The meaning of "you are beautiful".

I watched an American TV show yesterday, in which a man said "you are beautiful" to a woman.  This seems like it means "I like you" or "I love you". I asked my English teacher about this, and he comfirmed it, but he didn't know why it means "I like you" or "I love you".  Who can tell me why?

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Saying "You are beautiful" to a woman does not mean "I love you."

Saying "You are beautiful" to a woman is a bit stronger than "I like you."  As Stacie said in the comments, it is a way to flirt with a woman.  If I say "You are beautiful" to a woman, I am telling her that I am attracted to her.

However, context is very important here.  If the woman is wearing a new dress, she might ask, "How do I look?"  If I reply, "You are beautiful," it is only a compliment—I am not flirting.