I dont love playing NTR/NTS genres so answer of this topic will decide if I will play or pass
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There are ways of sharing the girls or keep them to yourself, you'll be able to pick an option with almost everyone (there are some cases where you just join an already existing couple). They won't "cheat" (since you're aware of everything) on you if that's what you're asking, I'd say just play it and see for yourself, you won't get NTR scenes if you don't select the options, and don't be too naughty/flirty with Anna at first since that will leave her in the slut route
Even if you choose the main heroine to be slut there wont be NTR. It's basically just her behavior that becomes sluttier but she will not cheat on you. There's sharing content however this sharing is also of your choice, when you're prompted to make a choice, black stripes will appear on the top and bottom of your screen and often it indicates the outcome. The pure route she will be very much there only for you and wont bother knowing about others things unless it's special characters that even in pure route you can still chose to share her with them or not. While the slut route she is open to more thing like taking nude photos or accepting to be touched by others in the park or and gangbang in the starcon, but all that is ONLY and IF ONLY you choose so. She will never ask if she can do it on her own which means, you shape Anna however you like. I prefer to make her into the slut path but i dont share her or any of the others girls with anyone, making Anna my personal slut wife and the other girls my harem. This something that this game really did well it's how much freedom you have. As long as you dont touch the choices of sharing nothing will happen
There's one thing to clarify. there's 3 types of NTR. There's Netorare, which consist of the loved one from the main character being stolen or actively betraying him.
The there's Netorase, which is when the main character choses to share his loved one with other people, but the loved one will never actively go out of their way to betray the main character. They only do it if you tell them to.
Finally the best NTR type, the Netori. In Netori, you play the part of the one person that will steal away the loved one of someone else. It's a type of NTR very little used in games and honestly to me it's the most interesting one simply because you play kind off the part of the "villian".
On the case of Starmaker, we can see that there's Netorase, whenever you choose to share the ones you love with someone else, live Anna with Ken, Adrian etc... and also Netori, when you choose to steal Alice from Adrian, or Katherine from the Mayor etc...
So in a just sense Starmaker is in part a NTR game too but not the usual one that 90% of game creators make which is the old boring Netorare type. It uses Netorase which is used often but not a much as Netorare, and also the rarely used Netori.
In your case the type of NTR you're looking for is the Netorare and this one wont be on Starmaker as Doc. Muramasa said