I disagree with the reading that Kanako is just using Akio and that the affection is one-sided in their relationship. At first, Akio was ready to reject the whole thing if the premise for their relationship was based on just tending to each other's wounds. However, Kanako reassured him that it wasn't so complicated as that: it was just that they were alike and yet different. To her, he was like that place in her memory - 'familiar, comfortable, warm' and Kanako wishes to offer the same to Akio because, while he doesn't admit it as openly as she does, he is also wishing for the same thing.
I think the disconnect might be coming from the contrast between the way they cherish each other? Kanako, being the older of the pair, is a lot more forthright with her wishes and demands. She's also a lot more impulsive and she makes her intentions known without first giving it a second thought. In a lot of cases, she jumps right in when she wants something and thinks about possible repercussions later on.
In contrast, Akio is a lot more reserved. He's afraid of making mistakes, being hurt, and hurting another person. He admits to being bad with other people so he tries his best not to get in their way. Initially, his stance toward Kanako was the same: he didn't know what to do so he thought that it would be best not to demand too much and to inconvenience her with his own needs. With her encouragement, though, he's learning to open up a bit more and to be 'a little more spoiled,' which basically means that he begins to ask her for things. It isn't that they're using each other, I think it's more of that they're leaning on/relying on one another - as partners do.