To support and maintain someone for sexual purposes: She has ''an old man'' who ''keeps'' her/ Maybe some day some guy'll even keep me (1560+)
“Agreement” is a better word than conspiracy, especially when you consider motive: to keep someone alive.
They'd have to keep someone to do nothing but answer the telephone all day.
Then, as if to keep someone out, closed the door and propped herself against it.
Madam Carrington said they tried to keep someone with them all the time.