I'll assume that since we're talking about Yennefer here, we're in book-lore territory and spoilers are a go. Skip the rest of my post if you haven't read the books! (though I don't honestly see how you could argue for or against Yen vs. Triss without having read the books :listen: )
i don't trust her and when i see her in Nilfgaard in TW3, imma off her like the rest of the BlackOnes.
Regardless of how you feel about Yen as a person, you can't forget that Ciri loves her like a mother. You may decide that your Geralt has a falling-out with her (though I submit that wouldn't be book-Geralt's attitude), but even then he'd remain overly protective of her for Ciri's sake.
Also, I'm not sure how much choice we, as players, will actually get. Don't forget: The Witcher series is a bit unusual for an RPG insofar as you don't get to choose the main character, and you don't get to make a certain number of choices you would in other games. In TW1, for instance, you can help the Order of the Flaming Rose if you choose so, but you cannot, in any way, join the Order. When Siegfried suggests you join, you don't even get a dialogue option: Geralt says no. A stronger example yet is the romance choices from TW1 to TW2. You can choose Shani all you want in TW1, but Triss is the more important character story-wise and you wake up in her arms in TW2 no matter what you chose.
Geralt of Rivia is not a character you get to define: he already exists, and CDPR gets the final say in what he does. You can change the world around him (one of the most awesome things about the game, in my opinion), but you can't change
him. And I get the feeling that, because Yennefer is an absolutely HUGE part of him in the books, and that his memory in TW3 should be near healed, you may not have any choice in this matter : CDPR might just go ahead and decide that Yen is the love of his life, the chosen mother of his adopted daughter, and that there is no scenario in which canon-Geralt would not go back to her.
Can't wait to see though :cheers: