Hana no Shizuku

Main character lost parents early, but recently his brother died as well leaving him pension house to manage. Hero has always been in love with his sister-in-law who later became his brother's wife.
A famous novelist was staying at the pension house and he asked main character for inspiration for his new lustful story. Main character persuades his sister-in-law to comply, and the pension house turns into lust feast.

[From vndbreview]