Nah I don't think that's realistic. Well that could happen in tv dramas like waiting forever coz your soulmates and no matter what happens you'll always end up together. Nah, real life doesn't work that way. Specially the one you love the most disappeared like that for years and you got no clue when or if they're really coming back. You're bound to go crazy if you keep waiting like that. It's definitely not easy to keep missing the person that you have strong feelings with. People are not superhumans to have all the time in the universe and just use it to wait for one person.
It happens in real life too. After all, aren't films and tv dramas molded based on human experiences? Also, how are you sure that someone who disappeared wouldn't come back? And it's only my assumption that he should've waited for Yoon. It's true that it's not easy to hold on to someone whom you're not even sure to come back, but wouldn't it be more painful to choose a wrong person at the end? Just my thought again...
Yes most films are often molded based on human experiences but it's pretty rare for an author to make characters as realistic as possible. And how sure are you someone who disappeared would come back? If it's painful for you to choose the "wrong person" over the "right person". Well surprise surprise there's more painful than that. And that is losing your damn self! That's why Taejoo and Yoon made such decisions for themselves. You can have multiple "right" or "wrong" person come to your life. But you yourself is the only one. Once you lose yourself you can only expect the worst of the worst things to happen.
You should have waited for Yoon, even if it took eternity.