I get what you're saying, but as the author, I only intended for Dave to show up once. I don't have anything I want to say with him, so I'd be purely giving him a relationship route, not because I am passionate about writing it but because others want it.
It's not NTR or cheating if you aren't together. If I were to write a Dave route, it would be incredibly short and a game over.
Not to mention, you can skip watching that scene, and I have already said in the next update skipping the scene also skips the silly aftermath.
I apologize that it affected you in that way.
I don't think you should apologize, at least not for this reason.
In any harem game, it will always be a problem for any character who is not an MC to have a sex scene. In this case, it was much worse because the character, before that, had a relationship with an MC. Even though the game made it clear that it was a spur-of-the-moment thing.
(I don't think it's right for people to come here and say that they felt betrayed by a secondary character.)
However, the comparison with NTR is not illogical. We can both agree that Greg's appearance makes the scene taken out of context resemble that. Dave's fans or just players who don't like this genre thought that was what it was about, and thought: "I'm in danger" or "Dave is in danger."
But instead of saying that they didn't like Greg's appearance and that it gave the illusion (even though it wasn't) that it was NTR, they prefer to accuse you of being a liar, which I believe is an unfair accusation.
Just like the rest of the LIs, Dave's sex life that isn't related to the MC or the harem doesn't interest me. Unless you want to include it as a demotivating element to produce rejection of Dave (I don't think that's the case), talking about his sex life and showing it may have been a mistake.
In my case, I just found it an unnecessary focus on secondary characters. If it were in the past, this would probably have stopped me from buying the game since I don't like to see sex scenes with other characters that aren't related to the MC or the harem, but since I already bought it, I'll just ignore them.
However, it all depends on the point of view, the people in this community always give their honest opinions about your product. They're not always the nicest or the smartest, but they give you a lot of feedback on what they DON'T like about your game.
(Even though some are pretty idiotic, it should still be taken into consideration)