Or WHAT IF--and I know I get a 2x4 for this--his friendly little email was a reaching out?
How am I to know if a friendly email from him is him testing the waters, or just luxuriating in the joy of me pining for him while OW satisfies all his other needs?
How do I know?
We don't know at this point. Your response to him was fine. Try not to get caught up in "what if" this or "what if" that. Worry can become a dangerous habit. If you would have responded in a different way, then you would be worried if THAT response was wrong. The issue here is not what you said, but in the worry and second guessing of it.
If he was testing the waters then your response was fine and he will test again. If he wasn't testing the waters, then your response was fine.