This is kind of tricky, but I've been jonesing for a threesome line between a wife, husband and a third party, preferably younger. Could be a young nanny, could be a girl from the office, could be anything else. I'd like to find one person to play the couple and we can discuss more exact details together.
Also, and maybe even better, the couple could be two men who are bisexual and the younger character can be either a female or a male. Whatever you're up for!