I think you're doing great. I think if you can, table the discussion about the email. He'll try it again, hopefully at a time when you can approach the situation. If/when he does, you can address how it makes you feel disrespected and inadequate.
I think the best thing you can do before he leaves is be pleasant and uninterested in his trip. Act as if...
Make some plans w/ the kids for while he's gone and have fun.
Me: 34 W:33 T: 10 M: 6 S: 6 D: 5 BD: 5/14 Still together(ish) Not giving up: 7/14 D talk has slowed, a lot. Gradually working on things together. Still separate bedrooms. Slow and Steady wins the race.