Snape and Lily as friends- How could Harry not know?

[rowena_grunnionffitch]

No: HPFGUIDX 172684

  Given that he didn't find out about his Dad's best friends
until book three, and then only because of that final confrontation
in the Shrieking Shack, I find it very believable.

  Besides it seems clear that being put in opposing houses distanced
Lily and Severus. Lily says nobody can understand why she even talks
to him; and no doubt he caught a lot of grief from his DE associates
about his attentions to a 'mudblood' Gryffindor. I doubt anybody but
the two of them knew how close they'd been as children.