I respect your opinion on multiple partners, but that scene shouldn't be specifically labeled as NTR. It currently plays out as a spontaneous consensual threesome. There is no dialogue of betrayal, a comparison between lovers, or anything unwanted by the unknown girl or her friend that would relate it to NTR.
We can suggest that the developer add "(threesome)" or "(join)" to the end of the choice that causes that scene. Then it can be clear and avoidable.
You also should consider that many games are presented through the perspective of the main character. You may control certain paths and interactions in some games, but others are firm on the direction the developer(s) want the main character to go.
This game is beyond supporting sex-positivity with the main character choosing multiple partners, genders, kinks, races, and even ages. Hence the wrinkly hands throwing feelskies on dat ass. 馃槢 (fast skip really helps at those parts though)
My $100 phone ran it perfectly in both the mobile and desktop modes through Chrome. Looks like even ridiculously expensive computers need to catch up to the power of cheap phones.
