How do you know when you are in love and how do you know if the person loves you back?

In my last relationship, I have blindly done things that others has called me really stupid and I have realized only too late that I have been taken advantaged of. When I am asked however, if I love this girl..I find myself hard to answer. I really don’t know. More so, I do not know if this girl had loved me either because she just kept taking from me and she hardly ever gave back. I also ponder on the relationships of abused women. Most of the women that I know of who has experienced violence kept coming back to the man who kept repeatedly beating them. People would say that they are stupid but were they in love? How do you know when you are in love? How can you separate it from infatuation with the person? How do you know when the person feels the same way and how to keep yourself from being taken advantaged of foolishly?