Do you really want your husband or wife looking, joking and shmoozing with someone else’s spouse??? Its a new person with new stories, jokes and personality with someone else who doesn’t know it yet. It it just dangerous and it can be a problem – I wouldn’t suggest it….it can just get to be a problem if they start “diagonal dating”
It doesn’t have to be a problem – it just has to potential to be one. Don’t put yourself in an issue. Like emlf said – why give the Yetzer Hara easy bait???