So what are you supposed to say to person who says: "I love you", when you don't? Replying is silly, silence is awkward and your friendship is usually ends at that very minute. Sad.
And what to reply back when smb says: "I still love you", and you already don't? You just feel guilty being happy without him/her at that moment.
What are you telling to person who says: "I've been waiting for you", and you didn't think a minute of him/her all this time. And friendship which could happen is over, even have not started.