For the ask game, here's a "Yes, and" for you
Bolaire picks up little habits from his previous hosts, things like crackling his knuckles or constantly brushing his hair out of his face (mask? Idk)
Yes! And I think it started long before Thjazi came in the picture.
Specifically I have a hypothesis that how he treats hosts/bodies now is very different than when he first gained consciousness, that there was a time when he was more... joyriding? Communal living situations? At the very least the way we've seen him treat bodies now is NOT efficient and is actively harmful to him being able to keep his secret. And is very different from how he treated his first body, with respect and assumption of longevity. So... something changed somewhere.
So I suspect he started out reluctantly taking a body because he felt he had no choice, and then keeping it going for as long as possible, years if he could. That's far and away the safest thing to do for him personally. And then potentially experimented with something more symbiotic than parasitic.
It was only later when Thjazi saw it him as a combination interrogator/hitman/body disposal unit that he started to form this separation from the bodies he wore, partly to isolate himself from the terrible things he was doing, and partly because he was forced onto terrible people that he did not enjoy sharing mind-space with.
So from those early years, when he was more hitchhiking than anything....
A kind old man, by the name of Paul, gave Bolaire the world darling. He hadn't learned to hate yet, but he knew how much of the world was fearful of him and his siblings. Paul was was old enough that his husband had passed on to the afterlife before the shapers fell, and his heart was broken that they might be apart for all eternity.
He helped Bolaire learn to navigate the world of humans, and shared how to seek out the best in everyone. Toward the end he wondered if perhaps the Druids were right, that souls could come back to this earth instead of passing on to the next. He took to calling each person he met darling, the name he called his deceased husband, to remind him to treat all with kindness, because you never know who they are.
Remna was a younger halfing woman, and wearing her was like coming home, in a way. She was a little mad to begin with, and seemed to enjoy having company in her head. She taught him how to duck and weave among the shadows, to pick things up that people surely didn't need when they weren't watching.
He doesn't laugh as much, these days, but when he does, the little 'ha-ha' he does to himself reminds him of her joy in life. She also gave him his hair, showing him how something so distinctive, yet so easily hidden, could help sooth over perceptions.
An oddly slight orc, and the first body Bolaire wore who was neither male nor female. Vark didn't wear Bolaire long, just helped transport him from farm to city, to find a young man who was a more long term prospect. But they shared deeply of Runjani culture with him, and of the struggles of their people. It was the first time Bolaire had given much thought to his own gender, something given to him at creation, but not a command.
Although the idea of something in between was rather appealing at the time, it was not long after that Bolaire met Thjazi, and such frivolous thoughts of potential personhood were put away. It was hard to justify asking for they, when one was once again fighting not to be it. But once in a while Bolaire finds themselves using different pronouns in their own head out of habit, with the mental equivalent of handling spun sugar, and wonders if a time might come to trust again.