It works best only when cuck and Bull are good friends. This friendship between them is really important for the wife.
Both cucks and Bulls should understand this. Wife is emotionally connected to her husband(cuckold) and sexually to her Black Bull, if they are not friends she feels torn apart between her heart and sexuality.
I have faced those days and was not able to enjoy the arrangement. It had lost its charm. Those were the initial days, luckily my Black Bull was experienced and husband very supportive. Over, the year they are very good friends, and outside the bedroom or in public no one can make out they share also special relationship of Black Bull and cuckold.
Ideally, all (Black Bull, Wife or the cuck) can deeply enjoy this lifestyle if there some level of comfort, openness and trust between them, even Bull and cuck. This comfort, openess and certain level of trust are other words for friendship