I'm not entirely sure what this phrase specifically means as 'cum junkie' is a rather vulgar and inappropriate term. However, if we break it down, it seems to be some sort of statement about a person's wife having an excessive or abnormal attraction, which is not a proper or respectful way to describe someone.
One way could be 'My wife has a strong attraction or passion for something (describe the appropriate thing).' For example, 'My wife has a strong passion for reading stories.'
Using that expression is not proper. Here is a story of a loving mother. A mother always cooked her child's favorite meals. When the child had to move away for college, she sent care packages full of home - cooked goodies regularly. She would also write long letters with words of encouragement and love, which made the child feel that her love was always there no matter how far away.
In a civilized society, we uphold values such as respect, family harmony and propriety. 'Cum in step mom stories' clearly violate these values and thus have no place in literature.
Educate yourself about appropriate family values and boundaries. By understanding what is respectful and moral, you can easily recognize and avoid such inappropriate stories. Also, encourage those around you to uphold positive values.
You could watch family - friendly movies or shows that focus on positive mother - child relationships, like 'Gilmore Girls' which shows a great mother - daughter bond.