Florie, It's normal to have bumps in the road. Try not to beat yourself up about the email. I think your response was fine. Perhaps, you could add "Thanks for letting me know :)" if the opportunity arises next time.
It can't be easy to grin and bear it knowing he's out with OW. Could you aslo go out, at least for part of the night to take your mind of his "date"? (((Florie)))