This is why I always force the fact that netorare has changed over the years since its initial meaning, or pretty much just went back to its literal meaning.
Netorare isn't primarily about cuckolding, it's the "being taken away" part. Its why Netorare tag applies and is usually in "kid sees bully steal his mom" or "brother sees asshole steal sister" even though the MC doesn't like them like that, it's the feeling of being taken away from them. Does it feel objectifying to think it like that, guess so, but that's what's part of it.
So while Nick doesn't have feelings for Maya (he should they're great), some people here self insert as Nick, or see Nick as being Maya's love interest, so when she mingles with others, they feel "robbed" because its like she's being "taken away".
PinkMochi says he's not making a NTR game, that's fine, I think the voyeuristic part of this already satisfies some NTR people since some NTR works aren't really stealing and leans more into just the MC seeing main girl getting action.