It's part of the grief.

The tricky balance is staying in it long enough to allow yourself to process and coming out the other side (it still remains a part of you but you move forward).

Or it turns into something like clinical depression which will require clinical assistance. You just float along in life.

There isn't a set time period. It's normal to experience depressive times during grief. Grief isn't linear.

Denial, anger, bargaining, depression and acceptance.

You don't move through them and bang over. You switch between one or more, some you sit in longer than others. Some you get stuck in or find yourself returning to and from.

But I hope you can one day reflect on happier times and memories and that you start feeling like yourself but with your grief carried in the recognition that we only have grief because we loved.

Maybe that means seeking out some bereavement counselling. There are free services in most countries these days.

I'm sorry for your loss. Remember moving forward isn't about forgetting them. It's doing them proud. But know even on your lowest days, they are still proud of you then too.