It is when Dumbledore asks Snape if he still loves Lily, Harrys Mother, to which he replies with "always".

This key point of evidence shows that everything he did was for his love to Lily, having not wanted her death to be in vain everything he does is to protect Harry and fight Voldemort.

The only thing that made this difficult was that Harry looked like his dad, who Snape hated, but also that Harry had his mothers eyes, which made Snape feel more emotions than he could handle.

Yet, his actions were still very clearly defined.