Pip, you can't change what has already happened, no matter how much you want to. I'd be angry too, but I also know that anger can eat us alive.
Maybe set your mind on today, give it a new start and let his actions today represent the person he is trying to be. He's in rehab, that's a good start, and maybe a new beginning for both of you.
This is easy for me to say, and not always easy to do, but living in today can only be done when we let go of the anger from the past and let go of the fear of the future. Enjoy today, it's where we are.
Hugs