In the overwhelming majority of cuckold stories, the wife cheats on her husband with a man who has a bigger cock than he does. But why not imagine the reverse?
The scenario would be the story of a young couple very much in love, where the man has a really huge cock and the woman has a really narrow vagina, which makes penetration really painful for her. The man is of course frustrated, but he wants to see his wife enjoy being penetrated, so he starts fantasising about seeing his wife with another man who can give her pleasure. They find that man. Only, as with all such stories, things get out of hand. The woman takes great pleasure in her lover, even going so far as to agree to sodomy. (something she could never do with her partner). She also gives him deep throats, swallows his lover's sperm, which tastes better...
The scenario would be the story of a young couple very much in love, where the man has a really huge cock and the woman has a really narrow vagina, which makes penetration really painful for her. The man is of course frustrated, but he wants to see his wife enjoy being penetrated, so he starts fantasising about seeing his wife with another man who can give her pleasure. They find that man. Only, as with all such stories, things get out of hand. The woman takes great pleasure in her lover, even going so far as to agree to sodomy. (something she could never do with her partner). She also gives him deep throats, swallows his lover's sperm, which tastes better...