The biggest problem in terms of sorting this out is "Is movie cannon or not?" because the movies give us a basis for "Snape and Lucius Malfoy are friends to some degree or other" in the books, there is no basis for that, so when Narcissa shows up at Snape's door playing the girl card, it's like WTF?!?!?! So WTF in fact, that it rates a hysterical mention in a piece either Forbes or Fortune did on the 10 richest fictional characters. The lucius Malfoy blurb included the note that now that the man was in prison, his wife had been getting certain late night visits from a tall, thin, wizard with greasy black hair. At which point again, everyone went OMGWTF because a business mag was essentially writing fanfic.