Oh dear. I am so sorry you are going through this!
I think I'd tell him to leave.
I might also contact FIL, just as you had written.
Surgery? Well, your BF knew his surgery was coming up and he did this anyway. Why should you continue to take care of him? He's not looking out for your welfare.
I know it's a very difficult time. I am SO VERY SORRY he chose to do this.
My heart goes out to you!!!

WC