The customization options are a bit lacking;
Where is the option to tweak the nymph to be more like the player's type to more easily fit in as a temptress, big breasts alone aren't always the answer for NTRing a guy from his girl, sometimes it can be the ass, or even something simply like the color and length of hair on their head, or facial features.
Since there is no actual voiced lines, there isn't any reason to not have the guy have lines between him and the Senpai, with a setting to decide how he reacts to Senpai's seduction, ranging from holding reservations for the sake of his girlfriend, to him fully giving in to his new girlfriend/sex friend.
Also, I'm going to echo the same statement as said by a number of other comments before me, the guy has at most an average dick, which shoots the initial statement of the Senpai that the guy has a big package into the ground, as it should be something thick and long enough to at least poke out through the boobjob, and visibly spread her holes open, if it is going to be large.