For me, my most hated character is Lily Potter, Harry’s deceased mother.
I will never understand how people can do what she did. I do not understand how she can just cut off a friendship and stop caring for Snape. I do not understand how she felt it was OK to not only date, but marry, the guy who bullied her best friend for years. I do not care if they were no longer friends anymore, you just don't do that. Lily knew who Snape was, she had been friends with him for four years. Friends fight and say things they regret but if a friend is truly sorry then you forgive them because you care about your friends and love them. You never stop caring for/loving someone in my opinion unless you never really did in the first place.
When the scene is discussed (and if you're into "Harry Potter," you know this whole James vs. Snape vs. Lily vs. everyone else thing is discussed way too often), I don't feel like James was totally the bad guy in this situation. I firmly believe Lily was in the wrong too. She could have been the kindest and most loving person to the people she likes like Remus Lupin and Sirius Black. Lily could have been an amazing wife, mother and friend to the people she cared about, but you can not tell me she was a good friend to Snape. She flat out left him. She dropped someone who she knew was insecure and vulnerable. She held a grudge. To me it felt like she wanted to leave him despite him saying "Mudblood" and this whole situation was just an excuse to do that. In the books, the Gryffindors were the “cool kids” so who’s to say she didn’t drop Snape, who came from the rival house that everyone hated, so she could just be associated with those who were popular. There really isn’t anywhere in the book that even tells you that Snape was in love with Lily romantically for all we know and what I think is that Snape loved her as a friend. His only true friend. She did have a right to leave a toxic relationship though, but the only problem with this was besides being friends with “future death eaters” and like the dark arts there really didn’t seem like any other things wrong with their relationship. It also doesn’t make sense to leave one toxic relationship for another. I don't know if Lily fell in love with James because he actually changed or because she was an obnoxious Gryffindor too. She did not have to suffer or put herself in harm's way but the way she did it and the reason behind it I felt was wrong.