I'm sorry about your father. You (and DH) must know that your emotional resiliency is rather low right now because you are grieving. Cut yourself a break.
Don't bother angsting over the diary (though I'm not following whose it is) or OW's comments. It's better for her ego if she believes that he just went back to her kids, isn't it? So she may believe that, or WH may not have had the stones to break up with her outright, and gave her the "kids" line in order to still feel like a good guy.
I'd want to know what he said to her when he broke up with her. I'd also want to know why she's emailing him something personal. Does he plan on going NC with her? I understand he works with her, so NC has to be about anything personal.
In my mind, a WH who wants to rug-sweep isn't facing the consequences of his choices. He'd prefer not to do that. His preference does not mean that you have to allow for rug-sweeping.
I don't know that you need to know every detail. Do you think that will help you? I think it might be better to work on a list of questions that are important for you to know, and - if you think DH is where he needs to be to move forward - ask those to him. Maybe ask one a day. Things like "Why did you do it?" and "Did you love her?"
But is he where he needs to be? I know it would feel so nice to drop your guard, believe his words, and go back to your marriage. However, what message would you be sending your DH about how you feel about yourself if you did that? If he's allowed right back, what is to stop him from doing this again?
A remorseful man would feel awful about his actions, wouldn't pressure you to let him back before you were ready, and would understand that he's going to have to be uncomfortable in order to help you regain trust.
I don't think your DH is remorseful. I don't think he's looked inside of himself to try to understand that piece of why he did what he did. He may regret his actions, but I think it will be a losing proposition for you to let a regretful man back in. Until there's remorse, I'd be hesitant to open myself up to him.
