Don't worry. The world needs people like that. Otherwise, there would be no one for others to take advantage of.
OK. Let's try again. Feeling pity and/or empathy for ANYONE who is sad is a good thing. It is the loving caring thing to do. But it is trouble if you allow mean people to use their sadness and manipulate you and take advantage of your caring.
That's a rare gift that you don't see every day..
Actually, it comes down to a lot of things, who we are is controlled by our experience, and our experience starts from birth. The way we feel love as children often defines our interpretation of it. Quite possibly, thru experiencing high expectations and being given little to no praise, the individual comes to the conclusion that no negative experience is deserved, (physically or mentally), therefore, making it there responsibility to assist anybody, regardless of relationship, thru negative experiences. This is only one interpretation and may not be correct in your experience. However I encourage you to more self examination, should you wish to understand yourself, and control your personal experiences :)