^I don't think you even need to go the route of NTR tbh. In my eyes her husband would probably be pretty chill about Yu spending some quality time with Xu Fu, maybe if Yu discussed it with him first. One could just write Yu as more than being exclusively into her husband with a fan fiction work, and include Xu Fu in there as well. As someone who isn't NTR I simply see it as easily avoidable personally haha