My (19f) boyfriend (20m) told me he wanted me to cuck him

My boyfriend told me about his fantasy, he told me he was into being a cuck. And idk what to do now i'm just here venting tbh.

I didn't even know what it was and he had to explain it to me and it was so weird to me. I don't want to fuck other guys. He knows I like having sex with him, and he's not small or anything, so I really don't get it. I'm scared that maybe I don't value that much to him if he wants me to have sex with other men, but he's also jealous, so I really don't get where this fantasy comes from.

Anyways I told him I didn't want to do it and we've never talked about it anymore, but I don't understand if I did something wrong.

I kind of feel weird now being in a relationship with someone that wants me to fuck others, it's weird.

Am I maybe judging him too much? I still don't want to go with other men but maybe it's just a normal fantasy and i'm just making a big deal out of it? What do you think?