a new kind of NTR? I don't know, it would be better if he broked up with his girlfriend

Exactly.

I don't know how I should put this... I enjoy hentai with cheating tematic and some NTR but if the story has a actual plot and I have any affective attachment for the characters I just hate it. So I would enjoy it more if he dumped his girlfriend for that neighbor, but in the end I think is super hot and I wish to see more smut stuff like that ...