Adding opposite sex on social media while married.

If you're married or in a relationship and you get a friend request by someone of the opposite sex would you or do you accept it? I don't mean like the spammy accounts or someone trying to hook up with you. I mean like let's say you're in a group and you have conversations (involving other group members) and then one day he/she adds you. Would you accept or do you think it's wrong?