The way I see it, this is a world that is largely ruled by ruthless, cold and illogical egotism.
If empathy and empathizing means sacrificing yourself for others, then you will often find yourself in a weaker place than the person you helped. That being said, I think that empathy is a broad concept, and that a lot of it is needed to live civilized with other people.
Does empathy make you a weaker person? I'm tempted to say that your actions determine whether or not you are a weak person. My best advice would be to keep your own interests at heart and mind, while helping others who need it.