Q. An editor just changed all of my nervous character’s “Oh, dear” comments to “Oh dear” without the comma. Which is correct?

A. CMOS 6.37 (Commas with “oh” and “ah”) has this to say: “A comma usually follows an exclamatory oh or ah unless it is followed by an exclamation mark or forms part of a phrase (e.g., “oh boy,” “ah yes”).” Since your character’s “Oh dears” fall into the exception category (an exclamation or part of a phrase), your editor was right to delete the commas.