You could call it a moment of weakness. It was posted many times before but you must admit that she was sure that Geralt and Yen are together again
Triss is trully great and loyal friend to Yen :laughing:
Triss is slightly different than the other sorceress in this regard anyway, just take this description from The Sword of Destiny "Triss Merigold, chestnut hair, cheerful, ready to burst into laughter for no reason at all, like a child. He liked her. It had been mutual."
But also we remember this quote from Blood of Elves:
Triss had watched them both and was jealous even though it seemed there was little to be jealous of. Their relationship quite obviously made them both unhappy, had led straight to destruction, pain and yet, against all logic . . . it had lasted. Triss couldn’t understand it. And it had fascinated her. It had fascinated her to such an extent that . . . . . . she had seduced the witcher – with the help of a little magic.
So if she was capable to seduce him to check why her friend love this witcher...she surely can even act drunk to take the situation and be closer again with him... just re-read the Blood of Elves chapter and see how desperately she wanted Geralt back...is she different in the game? I'm not sure.