Just finished Season1 and Season 2 on a pure harem/no-share route (high loyalty, SueNoShare locked early), and I didn't see any scenes where Sue cheats on the MC – no sex, no touching, nothing behind his back with Theo or anyone else.
So I genuinely don't understand where some people are seeing NTR/cheating in the harem path. The only thing that makes sense to me as a potential complaint is Theo moving into Sue's house which happens regardless of path.