Imagine if there was a guy who found out that one of his quasi-girlfriends or fuckbuddies wants him to be the Bull for another man to get the "cuckold experience," similar to the girlfriend experience but more intense. The prospective cuckold doesn't want just any Bull. He wants one that makes himself and the girl more comfortable.
Trouble is that the main character, who she asks to do this, is very reluctant and uncomfortable with the whole scene. He's never been into cuckolding or anything that extreme before. It's never been his thing, yet he is coaxed into trying it, and because he made the girl and her other man very relaxed about it all, very comfortable, he gets sucked into it repeatedly until he witnesses her falling for the cuckold and getting engaged to him.
Now they want the protagonist to be their Bull during the honeymoon, as they trust no one else, and he is fully entangled in their lives long-term. Unlike the cuckold, our hero isn't asked to be faithful, and he would refuse if he were asked to be. He's just always awkward about it, though less than he used to be.
What would be interesting would be to write this story as a team effort, with one entry (mine) being the reluctant Bull's, another being the cuckold's, and the third being the lady's. Any thoughts on this?