Watching the last HP movie in the background and they just got to the part where they reveal that Snape was in love with Lily for the past 20 years, which drove him to turn against Voldy etc.
But that's kind of awkward and ham-fisted, right? Like, there wasn't really much in the way of building their relationship except some implied jealousy between Snape and James. It took a 3 minute long exposition dump to make it work, when they could've just revealed that he's actually been a good guy the entire time, just not one that disliked Harry because he didn't get to fuck his mom.