Why did you compromise his trust and read a very personal, legal document? I'd be more concerned with why you did THAT than anything else. You can't discuss this with him because you don't want him to know that you looked at it. That's something that you simply don't do. I came across my own father's will one day while trying to find something for him. I did not even unfold the papers. Why? Because that's crossing the line. It was none of MY business just like it was none of YOURS. And I was his own blood.
I'm sorry for being so harsh, but I would be very upset with my girlfriend of ONE YEAR for looking at something so personal. If he wanted you to see it, he would have shown it to you.