When Alicia found out that Aaron had another girlfriend that she didn't know about, she was hurt and felt betrayed, even though Aaron never said there was no one else and they weren't officially "going steady." Alicia confronted Aaron and said she didn't want to see him anymore. This event was a reflective turning point in their relationship.
Alicia was hurt, it all changed when she found out Aaron had another girl friend. That moment she found out, changed everything because she was hurt and felt betrayed.