u/unimatrix33

I can't remember if the woman was his wife or girlfriend. She tagged along with her female friend on a double date. Her female friend was on a date with one guy, who had also brought along a male friend.

The four of them went back to the wife/girlfriend’s home. The female friend and her date went into the bedroom to have sex, leaving the wife/girlfriend alone with the other guy. They started talking, flirting and eventually had sex.

Later, the husband/boyfriend came home without them knowing and secretly watched his wife/girlfriend having sex with the other man.