It’s to your credit that your girlfriend turns to you for comfort and support. You’re right that she needs your friendship and patience as well as your love. It’s not surprising that she can’t be intimate with you while she sorts out her feelings and takes care of things that undoubtedly stir up lots of memories good and bad about a long marriage. I understand that it’s hard to be compassionate when you have no reason to care about the guy and it’s difficult to feel her pull away from you for a bit. But it’s unrealistic and unfair for you to want this to be over in a week. It’s going to take some time. I doubt your girlfriend is feeling guilty. (I certainly hope not.) If you didn’t tell her you were going out to give her space, she might have felt abandoned. She may also be picking up on your disapproval.
I’m hearing some insecurity in your letter. It’s as if you think her reaction to the death of her ex is any reflection on her love for you. It’s probably not. You are also concerned that if the situation were reversed, she wouldn’t be there for you. If the circumstances with your ex are different, of course it would be different. If you don’t think she can be your best friend in a time of trouble, that speaks to a larger issue in your relationship that is quite separate from what’s going on now.
It’s normal for someone to want to talk out her grief when someone she once loved (and had a child with) dies tragically. It’s normal for someone to grieve what might have been. It’s absolutely normal for a mother to do her best to help her daughter process all that has happened. It makes sense for her to take on sorting through belongings and bills as a way to show her daughter how to be compassionate and responsible.
This is the kind of situation that tests what you are made of. If you can be loving, compassionate and understanding while she and her daughter work through their sadness and anger, they will be forever grateful. If you can’t, the relationship probably won’t survive. I hope you can dig deep and find a way to stay respectful, patient, and loving.
I wish you well.