Kumiko to Warui Musuko

Kumiko, a mother of two children with her husband, spends her days living in a cheerful household with nothing left wanting.

However, a housewife such as her had a secret that she could never tell her husband. The secret that she's keeping is that she is in a submissive, carnal relationship with her son Harunobu. When her husband and eldest daughter are not around, in the living room she becomes Harunobu's woman; showing him an obscene side of her that she wouldn't even show her husband.

(Source: DLsite)