Period- turn off for guys ?

I was with my boyfriend today who I recently got back with and warned him that I'm on my period. He promised he doesn't mind and that he doesn't care so i agreed to hooking up- after a while he got kinda freaked out and admitted it was the first time he was in a situation like that so we stopped. He was lovely and understanding and promised everything is okay but I'm worried I turned him off? Does anyone have similar experiences ?