yes! It's known as unrequited love.
Yes. (What Summer Wind said.) Love is not something that comes with conditions. You don't get to dictate to someone that if you love them they have to love you, and visa versa. That would be self-serving, and love is not meant to be that way. Rather it is supposed to be self-less (when it is in its true form) because it takes the focus off of me and puts it on you. Your needs become more important to me than mine, and when it is reciprocated, visa versa. "I love you if..." is not love.
Isn't it most of the time?
Yes it is love but not in the true sense of what true love is. Unrequited or one sided love is not the full picture of love. A person with a healthy sense of self esteem will want a love that can be returned in full measure. If love is the most important quality of life then have it with someone you can share it with.
that's a very good question! if you mean romantic love, then i'd say it's more like "obsession" or "infatuation".
Life's an illusion
Love is a dream
But , I don't know
What it is
yes, that's called unrequited love.