The thing about my Second Talon AU is that I like the idea of Zevran and Lucanis knowing each other before Veilguard because it's ripe with potential. I'll entertain the idea that Zevran has lost the Warden either due to the Ultimate Sacrifice or due to the Calling at this point. He lost someone who was either his closest friend or quite possibly his love interest, reader's choice on these options because I could work with it either way. Then, he returns to the Crows when Antiva faces the threat of a potential Qunari invasion. He doesn't return with the intent of "reforming" them for their own benefit, but he returns because they're essentially Antiva's defense system, and if Antiva stands a chance at weathering this storm, then her Crows need to be strong. When all else has been lost to him, he is Antivan first and foremost, and he cannot stand idly by to watch her fall to ruin. Even if that means he must return to his gilded cage in order to protect his home from within, then he shall. Maybe after all of this has been dealt with, he'll return to his life on the run. Maybe not, but he has to do something.
Befriending Lucanis isn't something he expects, but he's curious about him. He has privileges as a Crow that Zevran could only dream about growing up, but there's something different about him compared to some of the others, which is reflected in the company he keeps. It's no surprise that he finds allies in Teia and Viago, because all three of them stand out in the fact that they care. For Antiva. For her people. They're good at their jobs. They accept their roles as Crows, but they extend that role as a duty to protect their home from any threat, both outside and within.
So, Zevran meets Lucanis, the First Talon's grandson, and while this rich boy can come across as a little out of touch with your everyday Antivan at times, Zevran is more than happy to remind him who and what they're fighting for, just as Lucanis is ready to remind him that it's okay to be selfish and have someone care about him and his needs for a change. They spend time together over the years from the moment Zevran takes charge after Guili Arainai's death, and they grow close, often raising questions from others about Zevran's motives, which Lucanis tries his best to brush off. Nothing really happens romantically between them until the last year or two before Lucanis gets imprisoned, but even that is more of a "will they, won't they" dynamic than anything actually occurring between them. They're okay with being just friends, but the potential for more is very much there. Of course there is some uncertainty for both, Lucanis and his inexperience, Zevran and his history of loss when he allows others that close (Rinna, Taliesen, the Warden).
But then the chance is gone. Lucanis is imprisoned in the Ossuary. Zevran spends day after day trying to search for answers, but nothing ever comes from it. To tie in Zevran in the role of Rook, Varric finds him at that point. He's trying to hunt down Solas, and Bela passed along his name. Said that he would be the perfect person to help him find him. That his history with the Hero of Ferelden and the Crows could prepare him for almost anything they face. Thinking about what the Warden would do in his situation, Zevran leaves his second-in-command in charge, and sets out with Varric.
That's not even getting into the relief of Zevran finding Lucanis. The situation with Spite. All of the unresolved feelings between them, and the fact that Lucanis gets to experience that same loss that Zevran felt when Zevran eventually gets trapped within the Regret Prison for weeks.