When I first started working with my current therapist, she told me that she believed "the relationship" was important in my case, likely more so than any homework in between sessions or anything else. She did not use the words love, affection, or anything similar, and it didn't sound like she'd believe that of everyone who came to her. I was uneasy enough with what she had said, but I think I've become more comfortable about the idea with time.

I think there are too many reasons someone might seek therapy and different ways they can be helped to make some claim like "therapy can't work without love." I don't really know the difference between love and attachment/caring/affection, etc., and I'm sure if you ask different people you'll get tons of different answers.