Could you speak with your H face to face? Maybe it won't be so easy to tune you out like it is on the phone. He probably is watching a basketball game or something when y'all talk, so maybe he isn't getting just how serious it all is. Surely he wouldn't be so unfeeling if he realized that.
I know you're terrified of what is about to happen. I hope for the best for you and S, and I hope your H will step up and be a good father. Does your S have anything to help take his mind off it? Besides school.