At what point does unrequited love become obsession?

After four years in a semi-conscious state of agony, it comes time in my painful reprieve to ask if my unrequited love has turned into something more corporeal. If not, how long before these feelings do turn into an ugly obsession. First, as in any real case study, we must define these seemingly simplistic terms according to the Merriam-Webster dictionary.

Obsession (noun): a persistent disturbing preoccupation with an often unreasonable idea or feeling.

Love (noun): (1) strong affection for another arising out of kinship or personal ties (2) attraction based on sexual desire; affection and tenderness felt by lovers (3) affection based on admiration, benevolence, or common interests.

Obsession, itself, is quite easily defined, but Love, the one Universal and encompassing emotion, it seems has no clear definition. Supposedly, Love is different for everyone. But if love is so different, how can one know that the feeling is love, esp. in the case of Unrequited Love?

I suppose when it comes down to it, the line between obsession and unrequited love is very thin and is dependent upon ones views of such. Would I say that, in my case, my experience has moved beyond the realm of love and into obsession? At this point, luckily no. But unless I do something to change my feelings or avert my destined tragedy, I'm going to become Glen Close in Fatal Attraction. As it were, I'd prefer to be a Bridget Jones.