This is one of those bitter vanillas. It teeters on the edge of the definition. I would say overall it was right decision to not add that tag. And before anyone says anything, there have been forced vanillas. It is possible, but this one is a little different.
I like how the last two frames have the "Why?" hanging between them. Really adds a nice sense of ambiguity as it was so far the male protagonist who we assumed was the narrator. With the juxtaposition presented by that second to last internal-dialogue box, one is left wondering if the narration is, in fact, shared by both characters.
...Hmm, that ending.
It did have some semblance of Vanilla in there, but I can definitely understand why it's not tagged as such. With a title like that, you'd expect it, right?
Well, it was an interesting read, at least. I kept wondering if he'd stop being nice and just go full on rape or if he'd just keep grinning and putting up with it...And then with that ending, well, feels like nothing has really been resolved, which is kind of fitting, I suppose.