There's a list of things Chirrut doesn't need to know. It's a short list, because in general Chirrut feels he needs to know everything, and doesn't mind being known as the nosy one.

Knowing how his best friend, his... other half, died, exactly, in any detail beyond that he did so?

That's on the list.

Chirrut doesn't make a sound, mostly because he doesn't want to lose what breakfast he ate this morning.