You're in a happy, committed relationship with someone you love dearly. Last week, you ran into an old guy friend who you hadn't seen in months, and he seemed more than excited to see you. You exchanged cards, and the next day there was a friendly email in your inbox.
You wrote back some light chitchat, but before you knew it, he'd already responded. This time fairly flirtatiously. He's unaware of your relationship status, and he seems to assume you're single. Though he hasn't overtly said anything to make you certain he is flirting with you, you feel a little uncomfortable with the way this is going. Since you don't know his relationship status either, you don't want to mistake an innocent catchup session with something more, but at the same time, you don't want to give him the wrong impression. You're completely off the market, so it's an awkward situation to say the least. How would you handle this?