grieve over (someone or something)
To experience intense feelings of sadness or mourning due to a particular loss (often the death of a loved one). It's been years since my mother died, and I'm still grieving over her. I know I need to grieve over the end of our relationship, but I'm just sick of crying. You need time to grieve over what you lost by growing up in such a dysfunctional household.
grieve over someone or something
to lament and pine for someone or something. Now, don't grieve over a lost cat. There is no reason to continue grieving over him.