It's not NTR, if you're fine with spoiler see text below.
Basically, she died. You can see her dying in manga chapter 1 page 21.
after chapter 95 most women that sleep with him is adventurer. They're not his harem that keep with him like common isekai manga. The sex itself is actually more like transaction like in manga chapter 10, after they sleep with him and feel satisfied, they move on to something else (like noble marriage, journey to another country, etc). There's elf too, mother and daughter in one package. But it occurs much later in the story.