Someone else's dream is not about you at all, but about that dreamer. If someone says something about you in THEIR dream, "you" represent that other person in their own dream. On the other hand, if you dream that someone warns you about your partner, that is quite different and you should pay attention to your own dream. In this case, the "someone" in your dream represents your own mind which is trying to get you to recognize that your partner is not as wonderful as you would like to believe.