Grief. One of the most important things you could ever go through. Grief is a teacher and a judge, it can test you on how long it takes until you break. Now, when writing a book, you need your grief to seem realistic. Therefore, I recommend you use the five stages of grief.
Sadness- Make your character feel instant sadness.
Denial- Make your character deny the grief and make up a substitute.
Anger- Make your character angry about what happened.
Blame- Make your character blame another character for their grief.
Acceptance- Finally, make your character realize that this grief will come and go.
Yes, you can skip a few stages, it is bend worthy, but I suggest you use at least three of the stages. Don't miss sadness as your first, and acceptance has to be your last; it lets your character grow into him/herself.
With these five stages, your grief will be complete and ready to go. Add actions, fights, and different break downs between each stage.
this is where i ramble; have fun