If it were me, I'd tell him not to worry about sending her a message, that just seems a tad controlling even though you didn't suggest it. My friend's husband made her do that with an ex of hers and she was really upset about it and I remember at the time how awful I thought it was because there was nothing there but facebook friends and an email once in a while. It just came across as really insecure and controlling. Besides, it would make you seem more confident and mature about the whole situation. I know that I'm far less likely to do something that would hurt someone's feelings if I know they trust me 100%.
If someone doesn't trust me and I always feel like they are assuming I'm doing something wrong, then I think 'what's the point, they think I'm doing it anyway'.
But I think you handled it the right way and so did he so at this point, I'd drop it and just let him know that you're glad that you two were able to talk about it and get it out in the open.
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