By what you have written, I'm not sure he is doing the wrong thing by keeping his passwords private. And if he has agreed to show you something himself that's reasonable. As for the porn issue, do you really care? Or do you need to hear it's wrong to cement your decision to leave?
Porn isn't really a problem for us and if he looked (which I know he does on occassion) I don't mind. We also have each others passwords but respect boundaries, I don't read his emails and vice versa. I have alot of friends write to me personal things about their lives and I don't want him reading that stuff out of respect for them. He knows this and it's understood.
I'm not really sure what you are looking for, I think you have made up your mind and like you said, it's another thing in a long list of things. This doesn't seem like something you need to fix or hash out with him unless you decide to stay and work on it. I assume he knows this so sees no point in giving you his passwords.
Good Luck OP