ISO thos novel, I read a year back

male live-in son-in-law → wife cheats → wife/lover's men beat him → throw him into the ocean → presumed dead → private luxury helicopter rescues him → discovers he's the sole heir of the richest family in world → returns to his wife's house to retrieve his ID → encounters wife's younger sister → sexual encounter with sister in law.

The protagonist's name was probably Ethan or Kevin. It was almost like a smut scene with sil and mil (maybe). I only read 2-3 chapters.