I hated it at first but

wait 7 years does make sense if you think about it:
It's mentioned that Hansol had just turned 20 when he met Sungwoo and had just started university. He's currently in his first year at 20 y/o. Assuming his degree takes 5 years, he must study for another 4 years plus his mandatory 2 years in the military. There you have 6 years with both of them being apart, plus one year post graduating where Hansol works to save up and prepares things like language and other studies before travelling to the USA, it can easily take him 7 years before they can live together again. And I bet they kept travelling to see each other from time to time.