It plays on a Island with a resort. A group of girls travel to the island and find an own opponent. Two of the girls watch a couple withe the wife fighting the ex. One finds an opponent and fights her on the bed with the other girls watching and the two lovers of them fight out under the hot Sun which one has he better lover.
Please help to find it.
Sounds like Canami Island. You can find it here: https://www.hostboard.com/forums/f294/490734-looking-story-canami-island.html