There are two types.

Unrequited love exists in two forms: the love that is unreturned due to lack of feeling and the love the is unreturned due to lack of knowledge.
I remember that I used to think that unrequited love didn't exist. It was just some excuse people needed to use to explain their lust for another person. I think that everyone thinks that until they fall themselves.
I fell for a friend and it took me months after his death to even grasp that I loved him. I just knew that when he was around I was a better person and I didn't care what anyone else thought as long as he thought I was okay. Some days I would hate him because we would argue all the time. But the arguments showed that he wouldn't give up easy and that he was my intellectual match. Those two things I think are important to me. It made my time around him worthwhile.
I never got the chance to tell him to his face that I loved him. He knows now, because I now have the strength to admit that I was once in love. And I also think that that is what has helped me move on.
I will always regret that I was never able to tell the first love of my life how much he meant to me, but you can bet that the second love of my life will know that I love him. I won't make that mistake again.
See, I told you there was another kind of unrequited love...