I hear you but I have no idea who the other partner would be in that scenario. Would love to hear if you have ideas ^w^
Honestly I don't think there needs to be a 3rd in their situation cuz unlike with Simone, there are no woman likers besides Gray in Gabe's route. I would be fine with just Gray and Talia, like the scene in Mark's route with Simone and Gray in the bathroom. With how the story's going after the most recent update, I have no guesses besides like idk horny spell casted during their DND isekai arc, but stranger things have happened in this game.