I'm certainly no expert on this, but it seems as if you are struggling with what you fear rather than relaxing into what you love.
I'm pretty sure that is what I would be doing also. However, in the past when I have faced difficult things, if I could stop struggling long enough to force myself to thank God even for the bad things and understand that scripture that says, "all things work together for the good of those who love the Lord and keep his commands," I have been able to find peace.
You are creating joy, and making memories every day. Those memories, like being on the boat and Nathan's stories, will bring joy to you no matter what happens with John. Maybe you can focus on that.
I'm sure much of your time is spent in doctor's offices and such, but there is joy to be found even there if you look. Nathan, who sounds like a commedian in training, must bring great joy to both of you. And even the doctors are sometimes hilarious in their attempts to help.
Maybe you already are or maybe there is simply not enough time, but maybe you could keep a pad with you to make blessing notes just to remind yourself and John of the blessings that are in each day. Even on the bad days, try to remember that God is beside you and will work it all out to your good.
You are surrounded by prayers every day.