Halsin and abandonment issues
One thing I've come to conclude about Halsin's character, based on many parts of his story and some lines he says, is that he might have abandonment issues.
To begin with: he lost his entire family over the years to accidents and disease, per his writer. That's the kind of thing that leaves deep scars- watching everyone you love fade away over years, until at a "comparatively young age" you're the last of your family and turned over to the Druids to be taken care of. (His writer didn't specify an age, but if he was young enough to be "turned over to the Druids" instead of "finding his way there" then it is likely he was not an adult.) There's no time to lose your family that isn't absolutely horrible, but as a young person is far, far worse.
Then there's Halsin's other traumas, all of which involve isolation; he was a prisoner for three years in the Underdark, and despite this, no one thought to come looking for him to save him. He lost most of his fellow Druids in the battle against Ketheric Thorm and the Shadow Curse that followed- and what few didn't die, he still lost their friendship to his leadership position, the "weight of responsibility". His one lasting friend in all of this, Thaniel, was lost to the curse and Halsin spent over 100 years blaming himself, fighting to be the best leader he could at the Grove, and having no one at all he could lean on for any of his burdens. And then he wound up kidnapped again, this time by the goblins, and when he returns, almost all his Druids have been turned against him, some even holding him in contempt. All experiences that are isolating in nature and reinforce to him that he can't rely on anyone else, that he is the only person he can depend on, and that in the end, everyone he cares for is going to leave or die.
It's not just speculation that he feels that way, either. He has several lines about his survivor guilt and isolation:
"[...] there is a burden to being the survivor... the witness to others' tragedies. It only grows heavier with time."
"[...] Grim as it is now, it was worse on the day of the battle. A vivid wound upon my memory. I was lucky - I lived, when so many did not. It would take me a day and a night to recite the names of all the friends I lost."
And lines that indicate he's used to being left, too.
If the player rejects him after he wildshapes (emphasis mine):
"Ah, I see. Well, of course. Back to camp then."
Saying "of course" implies it's not entirely unexpected.
After the final battle, if the player declines to have a celebration and says the party should split up:
"It was always destined to be so, if we prevailed. But the foreknowledge makes it no less bittersweet..."
He was expecting the party not to stick together.
Similarly, if a love-interest player breaks up with him in the ending:
"I see... After all my years of living, I know all too well that nothing lasts forever. Yet a parting can sting, nonetheless. But that just means what we shared was precious, and will live on in my memory. Thank you - I am a richer man for having met you."
The "nothing lasts forever" really sells it, to me, especially because the context makes it clear that he isn't just making a general statement- he's talking about relationships and people. Again- he was expecting it all to end.
His worry in the epilogue, when a solo-romanced player comes to the party with him, hints at this even more: "You could have done anything, gone with anyone... yet you chose me."
He's surprised that the player, even if they're in love, would want to live with him and share his dream. He can't believe they really wanted that- he even says that he keeps expecting to "stir from the dream".
I feel like that shows a lot about how Halsin feels after all the loss he's endured- he doesn't ultimately believe anyone is going to stay with him, whether because they choose to leave him, or because they'll die.
