How to deal with guilt of a parent.I left my mom on her death bed i am guilty as hell .?

She ask me to stay with her because she was afraid to be alone i told her that i had someplace to go and would be back she died the next day.those were the last words my mother said to me.I ask god if she can forgive me for my selfish act.how do i cope with the guilt i miss her every minute of the day.help my heart is breaking.