Lets talk Larkin Douglas.
AKA The most loyal man out there.
Most loyal? I hear you ask confusion ringing in your voice. I know Nick and Sel exist but let me explain.
Larkin Douglas is Loyal to His King aka Bree. He knows that Sel means a lot to Bree, so letting him go is a way to help him in the eyes of lark. He is not loyal to the order because and I quote:
"We were not friends at the academy, but we were not enemies. Our parents trained us in the old ways, to go beyond the title, beyond the Oaths in order to do what must be done."
He knows that Sel can protect Bree in ways he can't so letting him escape was a small way of helping both of them. They have matching tattoos, Lark probably views Sel like family, Lark is loyal to Bree. We see it again when he helps break her out, when he made her leather gauntlets that were imbued with aether.
Larks loyalty is shown in his actions, and everyone of those actions is to help Bree because Bree is his King and ultimately knows that she comes before him. Bree means more to him than any oath to the order.
I tolerate a lot but saying LARKING DOUGLAS is not loyal is wrong. That is who Lark is, I know y'all make jokes about him quitting on day one, but we all know that Lark would spy on the order for Bree. Lark is the Merlin you call if you don't want to get scolded or yelled at (Nick and Sel) when you do something wrong.
Larkin Douglas is what loyalty would look like if it was a person.