I will say I'm not big on NTR myself, but I also get that everyone has their own interests, admittedly I have avoided a few games due to seeing the tag on them. However, imo, so long as it's not a main character, or one you see a lot, I personally don't see any issues with it. I do sometimes like the side characters more than the main ones though, so it's a tad bit iffy. If it's a character you never see, or hardly ever see, then no issues with me. If it's something like I've read where you'd literally have to go out of your way to get it, and that it's optional, then sure.
If what I've read is at all true, which idk for sure, I didn't read through everything tbh, then a promise was made, but broken. It's honestly a common thing with games, sure not VERY common, but still common. This is the case more so with a game that's free, they will usually prioritize supporters, can't please everyone after all, and prioritizing them makes more sense, they are the source of income.