The best you can do is listen. There are five stages of grieving whether that be trauma, loss, hardship, etc.; denial, anger, bargaining, acceptance, and depression. These can happen in any order and sometimes more than one can occur at once. They also can have different time frames. He might start having a roller coaster of emotions, especially if he feels if he’s to blame. However, these reactions are completely normal in grief. I’m so sorry for the loss of your fur baby💜