Here's a hypothetical: an ex that you had strong feelings for contacts you on Facebook... just saying hello. They know that you're in a committed relationship and (if you do) that you have kids, but they just wanted to get back in touch.

Do you reply? Bonus points: if your SO got a message from an ex, would they reply?

ps This week I had breakfast with a friend who got contacted by his first real girlfriend, the love of his life. He didn't reply to her Facebook message because he's married with a kid and didn't want to go down a path that might somehow end up risking his family.