Other people have relationships in the game, some which are not to their liking (e.g. Nalla being abused by the Baron which you can avoid by not even talking to her about it or kicking out the Baron and having her to yourself), others are quests which you can set them up together (e.g. The Nun and the Pastor Fox or Mr Grimm and Lala bunny which have alternative routes which are avoidable). Not everyone in the game is single and for the MC to bang. Some have husbands but ultimately prefer to sleep with you. I don't really know what number ratio I can give because this 3 letter word has really caused me a headache and I really don't know what falls under that category anymore, but in my opinion it's less than 40 percent.
NTR has 3 subcategories, but it's used here in a completely different way so that doesn't matter.
Basically the things that annoy people will be a potential love interest having sex with another character, being stolen from you, them sleeping around, you having to whore out a character, and forcing characters together.
Most
reasonable people will not care if a character is married/ in a relationship as long as you the player are stealing them away or cucking the husband, boyfriend, or potential suitor.
Also characters don't have to be virgins or chaste, but if they sleep around after getting with the MC you will annoy people, like how it's mentioned the woodcuter would sleep with the cat bandit lady is fine, but say that they it continued to happen after you beat her that would annoy people.
You can if you want also have some characters that you don't want to sleep with the MC ever, this may annoy people but the majority will be fine with it if the MC is never interested in her or you are helping a character people actually like.
Generally what you really want to avoid is doing what you did earlier and having it where to progress a quest you needed to whore out one of the girls to progress the quest, I'm aware you added the other route later to do it a different way but I highly suggest you don't include quests until both options are available at once to avoid the headache.
Generally if a character that a player wants to fuck is fucking someone else it will annoy a lot of people here if they can't stop or prevent it. There is one type of NTR some people are fine with and that is if you fuck up and lose and then you get the girl stolen away because of your own failure as a player, but this will still piss off the hardliners.
No matter what you do you will annoy the people who refuse to see another dick in a video game, but ignore them and just try to please the reasonable people that won't bitch at you for a game having avoidable content that they don't have to see