Whichever was the case, Snape didn't need to actually be with her to fall in love with her. I would guess that Lily (and Harry's eyes are a living reminder of her) might have made Snape lose ...
However, when watching the scene over, there are other clues that viewers may have missed. Snape, then, protected Harry out of love for Lily but inevitably projected his hatred for James on him. All ...