Author is a fucking coward. Literally shows page 39 and then boyfriend MEETS andSEES an unkown man enter his gf's place and suspects nothing? What's the point of showing them then?
This feels unfinished. If there isn't a second part why bother with show any of this from the boyfriend's POV. If there is a part 2, I feel like the boyfriend will end up with the Ponytail girl, maybe when she comforts him, because if h doesn't figure it out in part 2, WTF. I would bet she's still wearing the necklace at the end when they meet up, annoying they didn't show that or the boyfriend's reaction.
By searching this one's title I found another good story in a NTR blog, https://eroitaiken.blog.jp/archives/79818763.html, the plot is kinda touching in a realistic way with a little drama, I hope there is one like this.