Katei no Jijou de Osowaretemasu

Yuuma Kuroki leads a normal life as a salesman at a bank. But, one night, he's taken into a hotel room by his favorite celebrity, Kanade Nikaidou. Kanade pushes Yuuma down onto the bed and mounts him... Yuuma's mother suddenly tells him she's remarrying. As if that weren't hard enough, his new dad is his boss! As he heads home from work surprised and confused, Yuuma encounters Kanade, who leads him to a hotel room. Later, his new dad introduces him to his new brother... who turns out to be Kanade!

A complicated relationship commences between the two new brothers.

(Source: Shusuisha, translated)