Tonatsuma!

Nao moves into an apartment building to live on his own because of his father's change of job. His mother has asked her friend Aoi, who lives in the same complex to look in on him from time to time. Aoi ends up doing much more than that as any time he spends with her, whether it's unpacking, shopping, reading, or anything else usually turns into hot sex. Normally, Nao would be thrilled about a new life full of sex with a beautiful and lusty older woman, but Aoi is a married woman.

(Source: ANN)