Why didn't Raylan just kill Boyd?

They dug coal together.

------

Wait a minute... who am I here?

Why doesn't Batman just kill The Joker?

They dug coal together.

And there's history there, and history matters in Harlan. Raylan and Boyd were a lot a like and, at the end of the day, they had respect for each other.

In the second season, Raylan has a conversation with that mining executive concerning his relationship with Boyd. After hearing it, you would understand why he didn't shoot him.

It wouldn't have been Justified.

Because at some point while they dug coal together, Boyd saved Raylans life.
For men with purpose and pride, that means alot.

Its also why he didnt kill him in the pilot, and said he was sorry after that fact.

I love the fact that someone liked it to Batman and The Joker.

Personally I think some part of them likes each other company and would be bored without the whole cat and mouse element.

Personally, that's one of the fascinating points about the story that I love the most... Why doesn't Raylan just shoot Boyd? The real answer is that the show likely fails without the other. In the context of the show, Well I think the final scene in the finale explained that. Despite everything that happened, there was and always will be a mutual camaraderie between the two, regardless of who they are as human beings (Raylan a cop/Boyd a criminal.)