On the 8th of January Utterson had dined at the doctor’s with a small party; Lanyon had been there; and the face of the host had looked from one to the other as in the old days when the trio were inseparable friends.
There are no more uses of "inseparable" in the book.
Show samples from other sources
They are inseparable companions.
The Chinese think of Taiwan as an inseparable part of their country.