you could free him, and he’ll join you in the raid.
If you play this correctly, Halsin will fight alongside you.
However, he will not join you as a companion until later in the game.

In Act 2, you’ll arrive at the Last Light Inn.
This prompts a quest from Halsin.
Prepare for a tough fight, after which you’re able to recruit Halsin to your party.

This will lead to you a racy scene with Halsin.
That’s everything you oughta know to romance Halsin in Baldur’s Gate 3.
Former contributor Emily Gera also works on it.