In general, a relationship should be based on respect and positive communication. If these stories are likely to make the other person feel uncomfortable or violate the boundaries of propriety, then it is not suitable. It's important to ensure that any conversation between husband and wife is conducive to the well - being of the relationship.
Well, if by "black cock stories" we mean something positive like stories about black - feathered cocks in a cultural or historical context, for example, tales from a region where black cocks are considered symbols of something good, then it might be okay for a wife to share with her husband. However, if the intention is vulgar, it's clearly not acceptable in a healthy relationship.
Forgiving him depends on a lot of factors. If he is truly remorseful and willing to work on the relationship, it might be possible. But it won't be easy and will take time.
One interpretation could be that she heard some interesting folklore or stories about black cocks (as in the bird) and wanted to share. Another might be that she misinterpreted something and didn't realize it could have an inappropriate undertone. Or perhaps she is using it in a very specific cultural context that the husband may or may not be aware of.
If you've caught your husband in such a situation, first, take some time to calm down. It's a very shocking discovery. You could consider having an open and honest conversation with him about why he did it, your feelings, and what it means for your relationship.
Suppose the husband and wife are artists. The black cock could be their muse. The husband might be inspired by the black cock's elegant strut and shiny feathers to create sculptures, while the wife could paint beautiful pictures of the black cock in the yard. They could even name the black cock and it becomes a beloved part of their creative and married life.