Is it possible to build a relationship only with Triss, or according to the plot, Gerald will still stay with Yen? (The Witcher 3: Wild Hunt)

Well, based on the books, Geralt loves Yennefer, and Triss was his temporary lover at the time he was in a quarrel with Yen. So, most likely, everything is already predetermined in the game. Although I am also more for Triss, the character of Yennefer is simply disgusting to me.

Yes, you can

You can, confess your love to Triss, and Ian sends you off and that's it)

To whom Geralt confesses his love, stop and remain, if he confesses to both, he will remain alone. As they say, he chased two hares with x *** m left.

Interestingly, Ian fell in love with Geralt only because of the gin and Geralt's desire)

Timur Virinsky,
of course, I didn’t read the books to the end, but I wouldn’t say that it was only because of desire that she fell in love with him, although maybe because of desire, but I am inclined to believe that even in the world of the witcher, even a genie cannot create such feeling like love

gggggh134668
According to the plot, if you do additional tasks with Yen on Skellige, this chip of genie's love will be revealed there, etc., well, I won't spoil it)))

Timur Virinsky
Actually, the genie only intertwined their destinies. They did not stop loving each other after the spell was canceled.

JackofShadows
Another expert who knows exactly how the last wish works. And after canceling the desire, the player already decides. The developers did not just introduce this quest. Everyone decides for himself whether their love was true or imposed by a genie.

Geralt seemed to want to tie their fates, since the genie wanted to kill Yen.

Bust-Just
I know I did this quest, but after the gin, Ian says nothing has changed)

gggggh134668
Well, that means love, everything is fine, happy end)

gggggh134668
Both Triss and Ian love him, and who he loves is up to you and only you to choose :)