Snape was definitely conflicted. obsessed (yeah that is exactly the word) with Lily, seeing her living the life he wished he had, then they both go to the same school, and she's the only one remotely nice to him. Him having serious impulse control issues, which seem to still be around, which causes her to break off even the tenuous relations they had. To get back at "them" he joins the death eaters, but the old obsession comes back fast when he finds out Lily is a target. Impulse control, or lack thereof, he effectively sells his soul to Dumbledore to save her, she dies, but Dumbledore is holding him to his word. a decade later, Potter's son shows up, and Snape is trying like mad to hurt him like his father hurt snape. Dumbledore having to remind him what seems like every time they are in each others' presence, that he is Lily's son too... Hates him, but helps him when there is no other choice. and yeah, impulse controls still not working. serious playing of favorites in all things Slytherin.