Hi Julia welcome to PC. What you have shared experiencing is very traumatic. Caring for a human or animal you love until they pass away in front of you is extremely hard. It’s understandable you are having a hard time processing all that you are feeling.
Please know that even though you could not prevent his passing he was very lucky to have someone he loved caring for him until he passed.
You and your family are going to be ok. You should look into finding a therapist you can talk about how this affecting you so he can help you grieve and find peace within yourself again.
(((Caring gentle Hugs ))))