Book-Triss betrayed Yennefer and Ciri to the Lodge and is just one of many sorceress ****buddies of Geralt. He also sampled Fringilla Vigo and Coral.
Game-Triss lied to Geralt about Yennefer and made use of his amnesia to get close to him. Then gets butthurt if you pick Shani anyway. And in second game it's revealed she was scheming with the rest of the Lodge but didn't even realize she was considered completely disposable.
Yennefer's actions in W3 are extreme, but all to find her adopted daughter.