
Yep. After the first accident where both were involved, the family separated the two. They paid Hakyung what he was promised but Hakyung wanted to see Yoonsung at least once to make sure he is okay after the accident but his family refused. So Hakyung simply left, he left behind the money he was paid. He likely worked like crazy for his mother's bills but still couldn't keep her long.
After the second accident which was more of an attempt by Yoonsung his family sent him to US hoping he'll never gain his memories of Hakyung and move on. But Hakyung's mother passes away so in a moment of weakness? I suppose he dialed Yoonsung and simply cried his heart out.

uhm actually YE's family did not send him to the US. After YS's suic*de attempt, he lost his entire memories going back to Korea and he said he was suprised why he was in Korea (his last memory is him being in the US) That's the reason why he went back like usual. When he left that's where his symptoms began showing. The phone call Hakyung made to him made ponder if what he's looking for wasn't a woman but a man. I think iirc this was in YS's pov in the novel too
Hey bakas was that a flashback im confused