I accept every different opinion but from my point of view cuckolding is definitively not cheating (because the husband is always aware and often directly involved) and therefore not a sin. If the husband is not able to fulfill the wife's sexual needs (what is required for a happy marriage) he can not be enough thankful to the bull for his help. It would be a sin if the husband has only selfish intercourse with his wife without being able to give her any sexual pleasure or orgasms but using her pussy simply for another kind of masturbation. Also the chance to impregnate the wife when she is experiencing an orgasm is much higher, so a man who wants to impregnate a wife should only ejaculate while she has an orgasm, if the husband is not able to do so he should delegate this also to the bull.
On the other hand it characterized a happy marriage that a loving wife is also caring about hubby's sexuality, meaning helping him to avoid to sin with permanent selfish masturbations by caging his penis. Due to my experience managing the whole male chastity topic for the hubby is not only fun (sometimes it is) but also hard work based on knowing what is best for the hubby (selecting the right cage or different ones for different purposes, holding the key, controlling shaving and washing, setting up the right ejaculation schedule or making sure that the prostate can be emptied without orgasms for health reasons, dealing with resistance from hubby against measures which are only for his best and so on.