in which harry wont leave his room until he gets to see louis again

Harry Styles was diagnosed with multiple personality disorder when he was only sixteen. When his mood swings and violent streaks start to harm those around him, Harry's parents reluctantly send him to a mental hospital: Whittingham Asylum. There, he meets detective Tomlinson, who wants to understand the demons that lurk within Whittingham Asylum.

High school student Niall Horan's life turns upside down when London's most wanted criminal climbs through his open window one night. Trapped in his own home, Niall struggles to keep himself and his friends safe while battling his own mind. While being stuck between truth and lies, right and wrong - Niall must also prevent himself from falling for his captor.

Louis was the boy next door who was always outside and living his day to day life but Harry was stuck inside, for reasons he didn't like to share. His love for Louis was developed over years of admiration. (( my interpretation of Sign of the Times ))