Bitter
As far back as David could remember, he and the twins had always, perhaps instinctively, clashed.
When they were young children, before Francis was born, it had seemed most unfair to him that they were always together, always united, automatically on each other's side, leaving him the third wheel, the isolated point of a triangle, the one always left out or made to stand alone. In any game or activity they were a ready-mate team, younger, yes, and perhaps not as intelligent as he was, or so he attempted to soothe himself by saying, but nevertheless more powerful and able simply by courtesy of their being two against one. In any argument or battle, whether verbal or physical, they would be able to best him simply because of their relentless support for each other, no matter how underhanded or illogical their counterattack. David had no one to back him up against him, no one to turn to for relief.
And this was what made it harder for him, as they aged, as the twins' bond with each other, their union against him, only grew more intense and sophisticated, extending beyond children's games and play into a general philosophy of existence. He knew, observing them, living with them on a day to day existence, that nothing could come between them, that any efforts to do so by anyone or anything would only cause them to draw even more closely together to each other to block the intruding force out. They were each others' first and foremost.
David loved them, of course, and he supposed in their own ways, they loved him as well. But knew that no one would ever love him in the intent, symbiotic way that the twins loved each other, that he would never have the automatic understanding and support from another person that they had, the state of being as if another person were simply him all over again, a slightly changed reflection of himself in flesh at his side. He would never be someone's first choice and most loved, and he would never have another person that he himself felt so strongly for.
And as they entered the teenage years, then adulthood, and the twins' relationship with each other became progressively closer, then to enter the realm of sexual intimacy, David would watch them whisper into each other's ears, smiling into each other's eyes, would watch them walk with their arms entwined, and even if they did nothing more physical than this in his view, the suggestion was enough for his face to redden and his muscles began to tense as much with jealousy as with anger. He would hear the noises in their bedroom at night or watch their eyes flash knowingly when he walked past, eyes averted, and feel so intently about what he was witnessing that he could not bring himself to speak.
It was not the impropriety that truly bothered him, whatever he might say to them about it, and his suspicion that they knew this all too well and delighted in it only made it that much more frustrating. It was his knowledge that he would very likely never have a lover of his own, at least one whom he could be with more than one time on one night, one who would love or want him back even half as much as the twins loved each other, that made their daily displays with each other that much more difficult to witness.