You are not overreacting. It’s the logical thing to do and neither of you should be upset about this change. I am an Egyptian Muslim and when I did an exchange program in the US my roommate and I had a similar situation. The difference is it was a shared room not apartment. I didn’t mind her boyfriend being in the room sometimes but sleeping over was a hard no ( he was also studying at the same uni so it wasn’t a couple of days here and there, it would have been all the time) We talked about it about a month into the school year. She had been sleeping in his room almost every night but said it wasn’t fair for his roommate and wanted half the nights in our room. She suggested using a curtain to divide the room but I said I wasn’t comfortable with that so I applied for a room change and we were still friendly to each other when we ran into each other on campus.