"If you love two people at the same time, choose the second. Because if you really loved the first one, you wouldn’t have fallen for the second". -Johnny Depp
Yeah I love this one. I pick this quote because it was perfect for explaining why Geralt should be with Triss. Love and infatuation are separate things. With Triss there is no magic except the magic of true love and true feelings.
In the game you see two people who have so much chemistry but they are too afraid to explore. They are both bound by their crutches, Geralt with his long history but very shaky relationship with Yen and Triss being in love with someone she convince she has no chance of keeping.
Sometimes it seems like she questions her own right to happiness. All is fair in love and war and their relationship with Geralt is no different. It should be a battlefield between the two ladies to get and keep the Witcher they are both in love with.
With the introduction of Geralt amnesia and the loving romantic relationship that develop between Geralt and Triss over time, Triss and Yen are on equal playing field to compete for Geralt.
You can see he's struggles with old commitments and what he really wants for himself. Triss struggles with her happiness vs the happiness of others and alway places the needs of other ahead of her own.
Everyone around hims seems to acknowledge that she is better for him, Vesemir, Eskel, Lambert, even Letho and many others. Ciri is all grown up and it's time for him to find some happiness with Triss after walking the path for so long.
To the core Geralt is a Witcher, the best of the best in fact. IMO an ending that have him completely abandoning his swords seems way of the deep end to me. Taking the occasional contract and spending time with the women he fell in love with is the ending I imagine for a Witcher like Geralt.