chinawa I already mentioned this in the spoilers above.
Rick always took care of HM, always.
After she found out she was pregnant, the Su’s invited her to live with them. She stayed at the Su home until she gave birth to the twins.
She returned to the castle home and lived with her mother and children because she wanted them to grow up in their own home. The girls were adored by the Sus. They were also close to SY.
Because of this, SY thought there was no way HM would refuse him if he proposed marriage. He saw himself as a father figure in their lives. The girls didn’t want him as their father, they wanted to marry him lol.
On their 4th birthday, all of their friends were encouraging him that the proposal will go fine and HM should have let QC go. This part pissed me off because even HM’s best friend and QC’s best friend encouraged SY to propose. They clearly had no idea how deep HM loved QC.
Unfortunately for SY, QC came back before he could propose. HM personally introduced him as her husband to everyone at the party. He met the twins too. The best friends felt awkward because they were happy that QC was back but sad because SY’s proposal failed.
QC didn’t make things hard for SY. He appreciated that he took care of his family when he was away. The twins also told SY that they knew their mom wouldn’t agree because she loves only their dad. They felt paternal love towards QC, but they also loved SY as a potential husband for them.