Until he succeeds
Instead of constantly hanging out with Severus, Lily was now seen everyday with James. They started going out and were official two weeks later. Lily had eventually forgiven James, but somehow she could never truly forgive Severus for what he'd said and for what she knew he'd been doing. I guess she didn't know how weak he could be; how uncertain he always was because of James Potter. The time to decide his loyalties came in senior year and now that his former best friend was with James Potter, the choice only came naturally. However, just because she hadn't fully forgiven him did not mean that she didn't still care. She went to see him one night before they had one of those meetings.
"Sev, you can't do this!" exclaimed Lily, "You're a good person!"
"And you would know that how?" Severus asked coolly.
"Sev, we've grown up together! Just because your parents - !"
He cut her off, "This is my decision, not theirs!"
She backed off. "Fine! If that's your decision, then go ahead!"
She turned to leave and Severus' composure wavered. "Lily I-I…"
She paused and he stopped. He couldn't say it. It just wouldn't come out. Who would she choose in the end? No, it was hopeless. "Forget it!"
Lily put on a brave face and marched away, not looking back.