With the fact that the player can gain weight now too, I think it would be cute if there was a scene in day 3 where if the player and Kev have gained enough weight between each other, they just can't fit on the bed together, probably with some awkward/amusing flailing around and stuff.
As far as I can tell, the highest combined BMI between them, assuming the player takes every choice that makes either of them gain weight up to that point, is 68, so maybe you could just have the game check for that.