"It's YOU, at last!—AIN'T it?"
I out with a "Yes'm" before I thought. (10.8, 10.9)
Here's Tom Sawyer's aunt Sally asking Huck, "Is that you?" By now, Huck is so used to lying that he says "Yes" before he even knows who "you" is supposed to be. In other words, Huck will be whoever you want him to be. Just like your imaginary boyfriend.