Responses
He probably knew after a while or the guy just looked so much like a girl that its hard to notice.
Novel spoiler: he knew, and just didn't care. But he never let it show. Like he said earlier in the story when they were eating Popsicles, that one he likes something he never changed his mind about it.
How would the seme not know that the uke is actually a man when he was pretending as a girl?? That doesn't make sense...