what is the most important moment in the book it ends with us

I think the most important moment is when Lily leaves her abusive relationship.

After Emerson, Lily's daughter is born, Lily decides that she must divorce Ryle for Emerson's sake. As Lily considers her situation, she thinks: “Cycles exist because they are excruciating to break. It takes an astronomical amount of pain and courage to disrupt a familiar pattern. Sometimes it seems easier to just keep running in the same familiar circles, rather than facing the fear of jumping and possibly not landing on your feet” (360). Lily, however, does not want her daughter to have the same sort of relationship Lily had with her father as a result of abuse. Any love Lily might have had for her father was overshadowed by the hate she had for him when he hurt her mother. She decides it is best for both her daughter and for her to have a broken home rather than an abusive one. She convinces Ryle by getting him to admit that if their daughter were being abused, he would tell her to leave the abuser because she deserved better. After Lily has told Ryle she wants a divorce, she tells her infant daughter of the cycle of abuse: “It stops here. With me and you. It ends with us” (361).