That poster is making a joke. Cuckholding is a sexual fetish that involves watching your partner get fucked by other men. The word “cuck” is commonly used by alt right idiots who call any guy who disagrees with them a “cuck” insinuating that the guy who disagrees with them is less of a man and must be ok with his wife getting fucked by other guys.

So the poster is making a joke. Firstly about liking the OPs rap, secondly about “his wife’s girlfriend” because anyone who disagrees with alt right conservatives is a cuck.

On another note the whole cuck thing is pretty funny, as someone’s who has lots of friends who are professional sex workers and some are dom/subs or host swinger parties, they always say it’s the fat redneck conservative guys who either pay for submissive literal kicks in the nuts or watch their equally unattractive wives get fucked by a male escort. Normally after posting numerous ads online and not being able to find anyone to hook up with them and their shitty personalitys for free.