It's a strange and inappropriate statement. 'Cock' has a vulgar meaning in this context. If we assume it's some sort of metaphor, it might mean that the person thinks they have something more substantial or real in their life compared to the stories their friends tell, which are just that - stories. However, this is a very unrefined way of expressing such an idea.
Cheating is an unethical behavior. However, here is a fictional story. There was a wife named Lisa. She met a much bigger man named Tom at a local gym. Tom was very charming and always complimented Lisa. Over time, Lisa started to have secret meetings with Tom, lying to her husband about where she was going. Eventually, her husband found out through some suspicious signs, like strange phone calls and her always being late. This led to a big crisis in their marriage.
Well, in the world of literature, you don't often find such a blatant theme. There are so many other aspects of human relationships to explore. For example, love, trust, and communication between a husband and a wife are far more important and commonly written about. This kind of theme is more likely to be found in very specific, perhaps less - respected types of writing.
Using such expressions is not acceptable in civilized conversation. We can talk about things like building good relationships, mutual respect in marriage, etc.