There are person who cannot love you much as you love them, either they already loving some other people or they just look at you as a friend. Despite how hurt you could feel, despite the pain, you should be open-minded and understand their decision. I think it could possible to happen if the love is true and selfless. If the person is a loving one too, they can appreciate you and develop a feelings towards you but again, do not expect from them. Even if you gave a lot to the other person, we are still not in control about their decisions.