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.
I shouldn't have to go through these gymnastics in order to avoid a character that could potentially ruin my romance for me. I don't even like Shadowheart (sorry for the blasphemy in this thread), but please, that's ridiculous game design.