Come on. Really ?
Triss had no idea where Yen was. If Geralt came back, she must have suspected Yen could be back too. Yen and Triss are good, if not best, friends, with their point of conflict being Geralt. Triss knows Geralt has always loved Yen. But hey, now he does not remember her, so what ? He is mine !
Who cares that they have 20 year history, partially raised a daughter together and after enduring hardcore hardships finally got together? She is gone, he has no memory of her, I will make him mine !
As I said, I cant be too angry at Triss because she loves Geralt and unrequited love sucks.
But its still shitty from her.
And I completely understand Yen throwing out that bed