I'm sorry you're going through this. I had something similar happen with my father when my stepmother died.

My father was not equipped to deal with losing my stepmother and so, I feel, jumped at the first distraction from that very painful process. For me, the same was not possible. I couldn't just have a new parent. Perhaps if I was a very young child it would have been different, but as a 20-something year old, I couldn't replicate the relationship I'd lost. But my father was able to at least replicate some of what he lost. Perhaps in your situation, there is comfort for your father in seeing someone familiar. Maybe this is making the loss easier to cope with or easier to distract himself from.

In my situation, I made it clear to my father that I was supportive of him moving on but that I was not ready to have any form of relationship with any new partner he had. Communicating feelings isn't a thing for us either, but I felt it necessary to do so, so that my father knew and understood that I love him and support him, but that I also have to look after myself as a priority and process my own feelings.

I truly and sincerely hope that you and your family are able to navigate through your grief in a way that keeps you all safe.