It is your argument that is weak, since it is based on the notion that people can never change, which is not realistic. There are plenty of examples in real life where someone loves a woman, even for decades, and then ends up with someone else years later. There is no objectively "canon" Geralt, you are entitled to believing that he can never love anyone other than Yennefer, but that is still only your opinion. On the other hand, it is a fact that the choice exists in the game, and others are entitled to their opinion that Geralt can choose differently by the time of the game as much as you are to yours.
Just because they want that in the books, it does not mean it necessarily has to happen in the game. After all, the Witcher games are not about perfect happy endings anyway, nor about clear "right" and "wrong" choices. By the end of Wild Hunt, Ciri has grown up, and she lives separately from Geralt (as a witcher or empress) after the ending, while the latter retires. That is just how the story is written. You might not like that and prefer a "happy family reunion" instead with the three living together, but demanding the game to be changed to include that is indeed asking for fan service. The content in The Witcher 3 is finished, perhaps it would be best to accept the game for what it is and move on ?
No, I said nothing about removing anything, that is just hyperbole. The game obviously already includes the romance between Geralt and Yennefer. And the one between Geralt and Triss. And also the case where the witcher ends up alone. Nothing needs to be removed. But if something was to be added, however unlikely that seems now, then it should ideally take into account all those possibilities, and stay consistent with the concepts of the characters and relationships that already exist in the game.