So,is the lover of the duke (the white haired lady) not dead in this life? Like I couldn't...

I think she is dead ? and perhaps that's why naviah was put up for adoption, given the character they've painted for her idk if she left naviah to be adopted

But , didn't the Duke say that when she appears(the white haired lady), he will tell her about Naviah ? Or maybe I'm mistaken something

Based on what I've read, I think she left the manor for one reason or another (I'm also assuming that she's actually Naviah's bio mom so she was pregnant when she left which might have something to do with her leaving but that's all a big assumption ofc) and possibly promised to come back (or her "coming back" could also just be the duke thinking of the next time he reincarnates) but she probably died at some point after leaving (and maybe giving birth to Naviah leaving her orphaned)
So the duke doesn't have a confirmation of her death and he's able to see her again even if she did die in this timeline he can still see her again when he goes back in time, so she tends to be alive in his thoughts

I don't really know how the story is going to go of course but this is just how I've put it together while reading what's available right now

They’ve already met in this life, but then she left and said she would come back.(you can tell because the Duke speculates about mc might being his daughter, considering the time frame, but then gets rid of that idea. Meaning, they had spent a night together at least when they had first met. Which also means he met mc’s mom before already.)

I’m pretty sure mc was born via that timeline where he met naviah’s mother. Ever since she was born from that timeline, they’ve escaped from the duke’s time loop to the mc’s time loop.(that’s why he doesn’t know creed either. Despite mc knowing that creed was adopted by the Duke in her past lives. Meaning, the Duke hasn’t experienced the lives mc has experienced. She probably got the power to turn back time from her dad(the Duke) but only a few times cause she only got a bit of his time powers.(but not too much to destroy her body like his)

Now that mc is on her last time loop, it’ll probably switch back to the Duke’s time loops(unless he figures out a way to stop it on this life. Maybe the box mc’s mom left will have something to do with it?)

This is all just a guess based off what was said tho lol

Tl:dr;
The Duke has already met mc’s father cause he wondered if mc could be his, before brushing off the idea. The Duke has not experienced any of mc’s past lives, since he doesn’t know who creed is, nor any information about naviah.