Being in love is quite different from loving someone. Being in love bespeaks a deep-seated need which you believe you have found in that person with whom you are in love. A part of you makes that person 'larger than life.' This is especially so when that realization of being 'truly in love' occurs. Unfortunately, no human being is 'larger than life,' and when they fail in some way to live up to our ideal of what we think/imagine/believe them to be, delusion (one might say, reality) sets in. What we are loving or hating in them is a reflection of something within ourselves.
It isn't that they had 'feet of clay,' It's that we had our 'head in the clouds.' We can yearn for them, long for them, and suffer for it, because we are in love. But this need comes from our own insufficiency. It's a deficienty which we try to make up for by finding something "outside" of ourselves - humankind's most basic mistake.