I’m so confused what happened. He’s on a plane? Hakyung mom is dead what??

Flashback

this is showing the past, while yoonsung (who lost his memories) is boarding the plane, hakyung’s mother passed away

After the second car accident that made him lose his memories he went back to his study abroad. Hakyung mom was always sick, and the entire deal was for her expensive treatments for the hopes of a cure and provide better treatment.