DBD said:
..... They rough her up, and degrade her right in front of me, but it's consensual so what can I do.
Who are "they"? You mentioned your black wife was having an affair with her older white boss, but you didn't mention anyone else fucking and degrading her in front of you.
Anyway — if you find that disturbing, I would suggest talking with your wife, telling her that, and asking if all that verbal degradation and physical roughing-up turns her on.
If it does, and if both your wife and her boss understand that aspect of her sexuality, I would suggest telling her sex is one thing, but seeing and hearing her degraded in front of you is more than you can handle. I.e., it does not turn you on. Thus, you would appreciate her not expecting you to be present when she fucks her boss — and whoever else might be involved, if she has "degrading 3-somes" or "more-somes."
If verbal degradation and physical roughing-up does NOT turn your wife on, but she puts up with it because she feels she has to, I would suggest both of you talking with her boss and letting him know that both of you are OK with their fucking (if you are), but please cease and desist with the verbal degradation and roughing-up. He should have an interest in keeping your wife happy, because if she (for instance) sues him for sexual harassment, it could cost him and / or his company a lot of money.