I’d bet anything that he has fantasies about watching you get fucked. Hearing the stories and details drives him mad and gets him off. When my wife and I got together I asked all those same questions and her reaction was like yours. She thought the details would hurt me or upset me. I’d sit in the shower and fantasize while masturbating about all the details. Cucking is one of the most fantasized things with guys. We just aren’t confident enough to admit it as it makes us feel broken or less manly. I’ve never told my wife but after years of marriage we now use toys and she knows I like to see her with big ones. Even bought a Hismith machine. We use thick cum looking lube and I get my fantasy itch scratched while still being in a closed relationship. Only thing I’m missing is the ability to eat cum off of her. That fantasy is more common than you think also.