Zevran will leave Taliesen to the Warden if romanced and under 70 approval or friend zone and high approval, and if you don't choose "Zevran doesn't need the Crows any more." He will go back to camp where he has a special dialogue.
The Poptart Queen dang. This is my first play but I got how this worked pretty quickly and raised his real quick because I had to have him. So he sided with me as his approval bar was full. Sorry to hear that tho! Did you try again? I'm gonna try for Alistair next time. Or if I can't restrict myself, I'll probably do Zevran again lol