Pointless, I know.

What is the difference between love and obsession?
Who draws the fine line between the two?
Has it got to do with insanity?
When does a person who loves someone start becoming obsessed and stops being in love?
What is love?
Can you really call it love when it is purely a one-side thing?

Love [luhv] noun, verb, loved, lov⋅ing.
–noun
1. a profoundly tender, passionate affection for another person.
2. a feeling of warm personal attachment or deep affection, as for a parent, child, or friend.
3. sexual passion or desire.
4. a person toward whom love is felt; beloved person; sweetheart.

And so on.

ob⋅ses⋅sion [uh b-sesh-uh n]
–noun
1. the domination of one's thoughts or feelings by a persistent idea, image, desire, etc.
2. the idea, image, desire, feeling, etc., itself.
3. the state of being obsessed.
4. the act of obsessing.

dif⋅fer⋅ence [dif-er-uh ns, dif-ruh ns] noun, verb, -enced, -enc⋅ing.
–noun
1. the state or relation of being different; dissimilarity: There is a great difference between the two.
2. an instance or point of unlikeness or dissimilarity: What accounts for the differences in their behavior?
3. a significant change in or effect on a situation: His tact makes a difference in the way people accept his suggestions.
4. a distinguishing characteristic; distinctive quality, feature, etc.: The difference in the two products is quality.

Not what I was looking for.

1. the domination of one's thoughts or feelings by a persistent idea, image, desire, etc.

So technically, a one-sided love story is not quite love but obsession, eh?
Does that then mean that one cannot love if not loved back, since the definition of obsession somewhat outlines one’s feelings when “in love?”

Questions, questions, questions.