I am a 26-year-old heterosexual European man. I have been for four years in a monogamous relationship with my girlfriend. Recently she cheated on me. When she told me what she did, I felt a very strong pain, even stronger than I expected. After a few days of pain, however, I found that the sexual attraction for my girlfriend, instead of decreasing, increased after her adventure. In particular, I am now having a cuckold fantasy. I would like that she tell me everything she did, without sparing any detail, while we have sex, or that we try to play an actual cuckold game where she has sex with someone else in front of me while I give her instructions and tell her exactly what to do. My problem is that I am not sure what her reaction would be if I ask her to play out these fantasies. She feels very guilty and witnessed my pain when she told me she cheated. I fear that talking to her about these fantasies would scare her. I also fear that, as she is feeling guilty, she would say yes, but without really wanting to do this. I also don't want her to think I liked what she did when she cheated on me. I did not like it, but I would like to relive it in a playful way, in which I have complete control. How do you think I should approach this talk? Which reactions should I expect? How can I make sure that she is really into this if she says yes?
— Feeling Obsessed Replicating Treason & Dominating Adulterer
Cuckolding, like all fetishes and/or fantasies, is unique to the person and adaptable within particular relationships. But it's erotic humiliation — of the person being cheated on — that distinguishes cuckolding from hot wifing/husbanding or swinging. The cuck's partner, aka "the cheater," is in control, and the cuck gets off on having his nose rubbed — sometimes literally — in the evidence of his partner's cheating. (That's the theory, anyway; I've gotten lots of letters from women — and some men — who are married to very controlling cucks.)
Zooming out: Your reaction to learning you'd been cheated on — pain and shock, quickly followed by increased feelings of lust for your girlfriend — is not uncommon. It's less common for the cheatee to eroticize the betrayal; a couple may reconnect sexually in the wake of an affair, but rarely does a couple wind up incorporating eroticized infidelity into their sexual repertoire. But in your fantasy, FORTDA, you would be calling the shots, giving instructions, and telling your girlfriend what to do. That's definitely not a cuckold fantasy, FORTDA, and it may be a revenge fantasy.
But a cheating crisis presents a good opportunity for both parties to be completely honest with each other about what they want going forward. And that's what you should do, FORTDA: Be completely honest. First, make sure your fantasy is an authentic impulse, i.e., it's a genuine turn-on, unearthed by this revelation, not an excuse to punish your girlfriend for cheating. Make sure this isn't a revenge fantasy. If it's a genuine turn-on, FORTDA, share everything: this surprising new turn-on, your own confusion, and your legit concerns (you don't want her to agree to do it out of guilt, it's not a license to cheat).
She might freak out. She might be into it. She might freak out and then later be into it. (That's the origin story of most cuckold couples: Husband/BF proposes it; wife/GF freaks out; weeks, months, or years later the wife/GF asks if cuckolding is still on the table.) You can figure out the parameters later, if you decide to explore this at all, but it starts with a conversation. Good luck.