This topic: Side Chick is usually left for Stella Dimoko Korkus who knows how to tell such stories, but I'll try.
A side chick is a married man's mistress.
It's the man's choice to have a side chick.
The side chick is not always prettier than the wife. Sometimes, the side chick may bear a striking resemblance to the wife or a fleeting resemblance to the wife. The side chick could be the man's mistress because she keeps a clean house, unlike the man's wife who keeps a dirty house. The side chick may have access to the man's bank accounts, unlike the man's wife who receives weekly money from the man for the maintenance of running the home. The side chick goes on business trips with the man, unlike the man's wife who doesn't go on business trips with him. The side chick may have a child or children with the man, likewise the man's wife. The side chick may be seen as peaceful by the man, and sees his wife as a 'nag'. The side chick may want the man to marry her to give her the ring, or may want to remain the side chick.
The man's wife may or may not know the side chick.
The man may build a house or houses for the side chick and not allow the wife to have any other property; except the one he lives in with her. The side chick could be a University undergraduate, graduate, a secretary, or any female adult really.
Usually with such men, there are divided opinions - some will accept his having a side chick - some will not accept his having a side chick.
In some side chick situations; the man's mother is aware, maybe she doesn't like the wife. Maybe the man's mother is not aware.
So if one decides to become a side chick or is already one, they are adults.