Judging by the way the little hints and scenes that were placed in this story, it looks like she's going to have sex with him. The fact that she was pushing for sex with her boyfriend and she didn't want anything to ruin her orgasm shows she's a nympho. Her innocent look is all just a cover for her true self that the MC saw when she was having sex.
...Hmm, NTR, though? I mean...It's not like she was really his to begin with, and ending up with her childhood friend makes some degree of sense. Though I suppose seeing it from the position of the guy who loves her but never got her garners more empathy from the reader.
I kind of feel like this guy is playing the wingman for another person's story by being really nice and lending his place to them, and yet he's sort of suffering for it.
I'm not too sure what to make of the ending, but it was a rather interesting read, I suppose.
It isn't objectively NTR? I figure it's a sort of realistic scenario. And personally this hit me a lot harder than most NTR stories. I don't know why I bother reading these, it's just not worth it for me (but I paid for this... ;_;).
The very descriptive monologue was really well written, the art was amazing, the story progressed at a very nice pace, but that ending right there left a scar on me that will burn until I see what she did when she walked back to the closet.