I've been thinking about this one...
I don't know if it's possible for love to have a direct opposite, but...If there is one, I believe it would be hate, as simplistic as it sounds.
Both love and hate/anger are strong emotions, but it doesn't mean to me that they must be related and that to not have love means directly that one has completely absolved themselves of all feellings, period (indifference). Granted, ambivalence can be had, but I don't believe that just because a person experiences a strong feeling of hate that they must also love the object ( for lack of a better word), or must have once loved the object.
Indifference seems to me to be the blank canvas upon which life's experiences can paint brush strokes of any number of feelings that may be related or not...and can change..