I really do not know exactly why I dressed him up. It's a mixture of things I guess.
I, in my own opinion, am not a typical female. I have discovered that I can determine how awesome a guy is by his response to my painting his nails. If he lets me, he's worth my time, as a friend or boyfriend. (three guys let me last year btw)
Next, the first time he came over for a sleepover, it was intended to be a "sleepover." So, as a part of truth-or-dare, I put him in a dress, and was delighted that he did and played around with me. I treated him as a girlfriend, and for a while, I thought he was closeted gay, because of our intimate conversations and the things we did together.
And as I mentioned before, I feminized him so I wouldn't develop feelings for him.
I'm sorry, but I don't have an exact answer.