But this is meta but how to avoid having Halsin in your party while healing the land. Spoilers.

Interact with sleeping man

Find out that man wants the lute - there are a number of different ways

Bring the lute to sleeping man

Talk to Halsin in camp

Return to awakened man.

Help Halsin - who is acting like an NPC - kill the shadows so he can rescue Thaniel

Talk to Halsin in camp

Find Thaniel's dark twin. Persuade the twin to unite with Thaniel

Talk to Halsin in camp.

Never talk to Halsin again.