Was that ending supposed to be endearing or something? MC abandoned his gf, and hell the potential for incest with his mom (as twisted as that'd be, but is still par for the course for this story) and mending his broken relationship with her to chase after this woman Nanami, and she simply gives him the slip forever like that and disappears? Does she think she can ever find fulfillment in her miserable life ever again? Fate gave her a free ticket to happiness and she returned it.
What a horrible ending to an otherwise good story.