I'm looking for a Hentai I read a long time ago. It was only a chapter long but it had good art. The story of the chapter goes like this:

Four friends [2 boys and 2 girls] are at the beach. One set is a couple. The girl from the couple and the male friend leave the male of the couple with the female friend to get drinks everyone. While they're gone the female friend seduces the male into having sex with her. After they have sex the chapter ends with the Female couple and the male friend that went to get drinks in the bathroom having sex together and you find out they have been having sex the whole time and it's not the first time they've done this.

I'm wondering what the name of this is and, if it's part of a book, if there are any more chapters translated from the same book. Finally, I would like to know the authors name so I read more from him.

Can anyone help me out?

This is my Sig ..............................................................

I don't know the manga you're looking for, but you can try checking titles with the "swinging" tag at major hentai readers.
In case you don't know any readers with advanced tagging system, PM me and I'll name a few.