i finaly played it and gotta say, solid update, however, i if had one thing that i disliked was how the "cosplay" was handled, specially since, a much better, and overal logical choice was right there!
to me, the "he was into it all along" doesnt really make sense, on the contrary, i feel like it would be more interesting if:
when we ask for her to take him on a date, we could be given a choice, a) take him on a date, b) tell him you will go on a date IF he cross dress.
this would be a much more organic way to make "him turn into a her". hell, even the reason for him to accept is there, since he thinks she is pure, she could just say her mother wont allow her to go out with a boy, so if he is dressed as a girl, they could fool her.
from there, we could have her tell us that he enjoyed dressing up, and even was hit on but some dudes.(we could even have her be a little pissed off, because they were asking him out more than her). so he would naturally develop that side of his.
so when we do find the picture, and ask about it, he doesnt "do it", like it happens, but tells us that its his cousin, so even that, we could have a later choice, in either ask him to introduce us and have a more "make him realize he was a trap all along", or have us blackmail him and corrupt him into a submissive sissy.