An idea (for unconditional love)
• Addie adopts Sarah, but can't because she's too young, she gets Harry to sign the papers. Addie and Harry both take care of sarah and most of all each other.
• Addie still plans to do all the fun things this summer with sarah, and Harry.
•Addie thinks with all the time she spends with Harry; every single day, she finally sees she likes Harry styles.
•Sarah's cancer gets better so she can have a normal life again.
•Harry and Addie start to date (you can do whatever you want to make them start there relationship) also add drama between there relationship.
• soon the summer ends, but Harry has to leave for his tour. Harry dosen't want to leave Addie and Sarah. Harry asks if they can come, but Addie says no because she has to go to collage and Sarah needs to go to school.
•after the tour, Harry comes back.
I think that's enough ideas to help you make more ideas and twist for your story. I hope this helps lots for the book so, you can keep going. Good luck!