TL;DR; Overall, happy with how many views and constructive criticism I got. I heard lots of mean words because this is "NTR," but few boxes of chocolate should fix my mood. Lol.
Long version: Although I uploaded this without any ad, I still got a reasonable amount of views and download. Also, few people gave constructive criticism, which was valuable advice for me.
On the other hand, there were lots of backlashes. Lots of people berated me out of spite of the NTR genre. (It was bad enough that Itch.io deleted most of the ratings. Creators can't delete ratings (if they could, they would be able to manipulate ratings.) They can only enable or disable ratings.)
When I was writing this, I didn't think this would count as NTR. The girl has her harem, and MC is inserting himself in there; she is not a special someone to the main character nor childhood friend. Therefore seeing her banging other guys might be shocking to MC, but it shouldn't cause emotional distress. I see the NTR genre as a type of tragedy, where one explores the catharsis of emotional pain caused by involuntary sexual harassment of his or her significant other. If the girl MC likes don't like MC back, that isn't the girl's fault. (Also, let's admit it. The MC of this story is not likable. lol) I marked this as NTR because someone is offended about it. I still don't think this short novel truly counts as the NTR, but if marking it so would save someone's emotional distress, there is no harm in doing so. (Although now I am getting messages saying they got pranked because this is not NTR, lol.)