That man seems to me peer of gods, who sits in thy presence,
and hears close to him thy sweet speech and lovely laughter;
that indeed makes my heart flutter in my bosom. For when I
see thee but a little, I have no utterance left, my tongue is
broken down, and straightway a subtle fire has run under my
skin, with my eyes I have no sight, my ears ring, sweat pours
down, and a trembling seizes all my body; I am paler than
grass, and seem in my madness little better than one dead. But
I must dare all, since one so poor...
Sappho, The Ode to Anactoria (Fragment 2), as translated by H. T. Wharton (1895)
Limerence, as the social psychologist Dorothy Tennov first described it in Love and Limerence: The Experience of Being in Love (Stein and Day, 1979), is that subtle difference between loving someone, and being in love with someone. It is not the same thing as love, nor sexual attraction, though they can all coexist.
Limerence can wax and wane; sometimes it's a slight, barely perceptible interest in a person, and sometimes it is overwhelming, breath-catching, world-stopping. Some people will never experience it their whole lives, and for some, the sensation of limerence is addictive, their attachment jumping from one limerent object to the next.
Limerence is sometimes confused with the propinquity effect, or the mere exposure effect, or plain infatuation. It is none of these things, though propinquity and exposure may contribute to limerence. Infatuation has connotations of immaturity, irrationality and incomplete understanding that are not necessarily part of limerence: while infatuation is a form of limerence, limerence need not be infatuation. Severe cases of limerence can be seriously negative and dangerous, but one can be limerent towards one's partner of ten years (most would hope to be so).
The word limerence is young, but the study of it among researchers of emotion, sexology and counselling has seen a steady increase since Tennov first coined the term in 1977. It is also increasingly used outside academic circles: Google and Yahoo both show more than 20,000 results.
Like many new ideas in psychology, there are disputed aspects of limerence, though few good critical investigations of the idea (at least, not by authors other than Tennov).
When you were here before,
Couldn't look you in the eye
You're just like an angel,
Your skin makes me cry
You float like a feather
In a beautiful world
I wish I was special
You're so fuckin' special
Radiohead - Creep (1993), Capitol
I hear your name whispered on the wind
It's a sound that makes me cry
I hear a song blow again and again
Through my mind and I don't know why
I wish I didn't feel so strong about you
Like happiness and love revolve around you
Boy Meets Girl - Waiting for a Star to Fall (1988), RCA Records/BMG
http://www.isi.edu/gost/brian/elbows/limerence.html - The Symptoms of Limerence