They may be perfect for you, but you are not perfect for them. If you can love your family, or love your friends, why can't you love someone who may not love you back? Once you take a person down off of that pedestal you put them on and get to know the real them through and through, if you're willing to let them go because you know you love them and they do not reciprocate your feelings, how is that not love? They may be the perfect person for you, but you are not the perfect person for them and I believe that's where unrequited love comes from.