It takes a time. Nightmares are normal because there’s something moving inside you, deserved or not.
I’m also grieving the loss of my doggie. He passed away two months ago and I can’t still see a video of him without crying…well, indeed I don’t allowed myself to see a video now. I need time.

Some time ago I read an article about recurrent nightmares and it was advised to write them down. I guess the reason is to work on them somehow. When it’s about a loved being’s loss I don’t know if it is useful to do it.
I don’t know what else to tell you. I know nothing I could say it’s gonna help you. Take your time. As long as you need.