Hajimete no Hitozuma

Yoshino Kanako is happily married to Tomoya and they are preparing to have a child together. Everything is going great until Kanako meets with her father-in-law, Makoto, whom Kanako is already familiar with unfortunately... Something she never disclosed to her husband is that seven years ago she prostituted herself to abusive Makoto. Fortunately for Kanako, Makoto agrees to keep the secret on the condition that they re-establish their intimacy.

(Source: TMDB)