Oh gs, how difficult,he does sound very sensitive. The first thing I would do is to speak to him face to face if possible. Is there any way you can meet up before June?
I think its worth investing a bit of time now so that you can strike it off your list of things to worry about in June, IYSWIM.
If you can meet face to face, it might be helpful to spell out in a gentle way, what you need to to each day at the moment with DS, and how this will change and what additional tasks you will have and how long they take when DC2 arrives. IME, lots of people without DC who have little contact with small children have zero idea about how all consuming it is. If you explain this very literally to him against a background of wanting to build your relationship with him when you are in a position to be able to, he may understand a little better.
FWIW, I found DC2 so much easier to deal with than DC1, and wished I had had a bit more company that first week she was here, which is very different to how I felt for about the first 4 months with DC1. But then it was a much easier birth, I knew what I was doing with bf, etc etc, and of course I know that its impossible to know this until the event.