when someone says "i love you" to you, it only means two things, "do you love me too?" or "please love me too". and so you must realize that you are bound to hurt her the moment you can't reciprocate her love. even though you've been clear that you can only be a friend, you cannot stop the other from hoping that the friendship will blossom to something more. the burden then lies on you. to re-clarify, put boundaries, and make clear what the friendship entails. for any positive action on your end though done in the goodwill of friendship, can mean differently to the one in love. we've all been there. we love with optimism and strong hope/resolve of being loved back, super magnifying every littlest of nice gesture. meanings are in people not in words or actions. so don't ever believe that just because you can't love the other person back means the other will stop loving you. it may not be your fault, but you can lessen massive internal hemorrhage and unbelievable pain to others if you set the boundaries of the friendship you can only offer, instead of leaving it simply as, "let's just be friends.".