It is so hard when you don't have the answers to so many tough questions. Just try to make the most of each day and live in the moment. God holds you all in his hands and he only knows what our future holds. And that goes for all of us, not just those who are sick, although we think about it more acutely in those times.
My dad became quite cranky from the steroid and the Keppra. It did subside after awhile as he got used to them. We found many of the things he would say humorous and it doesn't hurt to have a good sense a humor about it as it lightens the load.
I am glad your husband is happy to stay at rehab without complaint. So much easier on you both, I'm sure. You are doing a fine job supporting and encouraging him. I hope things get easier as he heals from his surgery. I know he must love and appreciate you so much, even if he is not quite himself at the moment to say so himself.