A friend has fallen into the classic trap: She's down because her boyfriend hasn't called (guys – CALL!) and is reading about his Sun sign, focusing only on the negative. That sort of focus is one trap and not limited to astrology. The other is in thinking that astrology is only about Sun sign.
Your Sun sign is your core self, but is modified by the rest of your chart which involves other planets besides the Sun and other signs besides the one your Sun is in. Sort of like having a bunch of houses, all with matching foundations, but each house and its yard is different. That's why you will never be exactly like someone else with the same Sun sign as you.