There's this great quote from one of Zhu's songsCocaine Model that has long influenced me:
When I was seven, my father said, "Fashion fades, but beauty is eternal. Elegance is illumination. Blue is a language. Love and obsession is separated by a thin line, and that line is infatuation."
Let's broadly characterize human beauty as either normative or personal. Normative beauty attempts to please the norm (of which there may be several), while personal beauty attempts to please the self (of which there may be a few, but certainly not many). Normative beauty and personal beauty don't have to be disjoint, and both can be influenced environmentally. But personal beauty, when realized, is always elegant to the self; unfortunately, the same cannot be said for normative beautyFor example, consider the disparity between what is beautiful to the eye and what is beautiful to the touch..
Understanding how an individual differentiates things like this has a tremendous influence on their relationships. Whereas obsession decays into a desire to appease an individual's perceived needs, love is characterized by an understanding of their needs. These states are distinct, but may be subtle; perhaps that subtly is infatuation.