What’s the opposite of opposite?

For kids (and adults) who play the opposite game: hot/cold, day/night, etc., it seems like "hate" would first pop into people’s head as a response to "love." But I don’t think that’s a good answer. I think I’ve heard shrinks talk about love and hate being very similar in the amount of passion they stir up within a person.

If my sister-in-law cared, and if I felt like being generous with compliments, I would say that “apathy” makes a lot of sense. Love and hate are hot, whereas apathy is cold. But, I had something else in mind. The author of a book I recently finished argues for a different opposite to love. And it’s not asparagus.