I think the original poster may need to clarify his terms, because cuckolding can also be consensual.
For example, I dated a guy who liked to masturbate while watching me **** his ex-boyfriend, because it was effectively a live sex show, or as he described it, "watching porn live."
Under some definitions, he was cuckolded.
So what one would do or how he would respond depends entirely on just what he means by cuckolded.