http://www.onpoptheology.com/2014/08/harry-severus-david-danger-of-single.html
“Harry cannot hear the alternative narrative, one in which Snape is a complex, complicated man who has earned the trust of Harry’s own much-admired mentor. Only after Severus’ death is Harry able to hear – or see, rather – the alternative narrative, as Snape’s memories reveal a deep and unwavering love for Lily Potter and a steadfast commitment to protect her only son which resulted from that love.”