mdu - haven't been where you are yet, but I'm in agreement with Bond.
Changing jobs is not to be taken lightly, especially at your H's age. It's a big, big, thing.
It would be ideal if you could always have absolute NC, but you may have to think through how much you can bend this, and whether you can trust him to honor the spirit of NC. As you said, you will have to judge whether he understands why you need NC and if he can meet your requirement without leaving his job.
For example, if I were to insist on absolute NC between OM and W right now, (not that we're at that stage, but she does seem to have left him for now) she would have to quit the volunteer job that she does for the school activity. They attend a meeting together twice a month. That would potentially ruin the season for a hundred kids. Would I do that or trust W? Mind you it's only for a few months, but you see what I mean.
Now only you know your H and whether he is in this or not, but at some point, you are going to have to trust.
I would go to the concert.
I would not send the letter yet; you have some thinking to do about how you are going to manage trust going forward.
