Well crap, I was hoping for such good things for you with H's leave.
Ok - opening line about bad trip, it's routine, it doesn't count. blow #1 - he hasn't decided yet, that's good right? other times he's just gone to his parents. blow #2 - um, I won't say what I really want to say.... Could you suggest a video that S3 could take to class? Videos of his dad who is gone all the time would be so nice for him to have anyway. I would try to get him to view it from a 3 year olds thoughts who loves his dad and wants this rare opportunity to be able to brag about him. Don't let H get off the hook so easy about being a dad.
Was he talking from a bottle when he wrote that email? Is he stressed about spending 3 weeks with W and Child? Is it too much for him? Regardless, I agree, plan your life for you and S3. Invite H to join you if he'd like to come along.
Live your life while you are still living. Riding the trail less traveled.