bechnokid:

I always wondered how Arthur and Lewis would act if Lewis ever rejoins the group. I imagine Lewis would forgive Arthur, but Arthur cannot even forgive himself, knowing he’s the reason Lewis is now a spirit. As a result, Arthur would be a nervous wreck in front of Lewis and is terrified of angering him.

Of course, Lewis would be worried and wants Arthur to be comfortable around him again, so he’d help Arthur regain his confidence one step at a time.