Movies about (twin) brothers and a woman I saw when I was in Australia

I think I saw it around 2004. I vaguely remember the woman reached out to one of the brothers first, she reached her hand in his pants. I don't remember what happened after that, but somewhere close to the end the woman had to go somewhere on a boat/cruise? with the other brother, so the one she was with at the beginning struggled with all these sexual fantasies about his woman and his brother on the boat in which he basically gone paranoid.
Anyone?