So you are upset that Lae'Zel, who is a Githyanki, leaves the party and attacks you when you betray Orpheus and side with a mindflayer, the sworn enemy of her people? ...... Wow
You chose back in Act 1 and 2 to pursue the Orpheus Rebel path. You knew that Orpheus was the only way for her people to overthrow Vlaakith and achieve freedom. Yet at the critical moment you sided with the mindflayer? And you expected that she'd be cool with that?
Now true love would be you becoming a mindflayer so that Orpheus would live to free his people and that Lae'Zel would choose to stay with you, which is what happens. You make the ultimate sacrifice and you become the greatest hero.