Grief, also called Bereavement, is not understood in our culture.  When we lose someone we love, there is no specific time period for us to grieve, no rules that apply.  Only, that we must grieve.  Grief is personalized, it takes as long as it takes.  

There are stages of grief, made famous by Kubler-Ross, that we move through in grief.  These stages are not linear; we move back and forth as it takes us through anger, denial, bargaining, depression until we reach acceptance.  Grief needs to be acknowledged and felt.  Then, we can move on.