This is a very solid example of phone-style novel games, please keep up the good work! You have a lot of good HIDDEN NTR content in this game. You say this is a linear novel/game; I am unsure if the choices make much difference other than if the GF sends additional photos to you or not, but if they do, or if you intend to make variations on the game, i hope you make a variation that includes hidden NTR to the end.
To me, the beach scene where I can ignore the hand in my response and then on Vanilla's side there is talk in the discussion about
was really super powerful and great. Unfortunately, a few sentences later I had no choice but to ask Vanilla about a guy in the photo and would have more enjoyed playing the dumb guy (NTR?) or the guy-that-is-pretending-nothing-is-wrong guy (NTS?). It was still worth it though because that earlier part was intense.