I think that people saying the ending is unrealistic didn't understand the story very well: it is realistic (at least to me) because they both had and showed genuine care for each other: and it is not a guaranteed HE. They both dont know how this new relationship between them will work out but they're ready to do their best after all what happened. Even Donhuyn said he cannot change how he is and asks Sungho to accept him as he is and he says yes. Donhyun choosing Sungho also makes sense, he loves him because sungho needs him. It is a very codependent and dysfunctional relationship.
I think that people saying the ending is unrealistic didn't understand the story very well: it is realistic (at least to me) because they both had and showed genuine care for each other: and it is not a guaranteed HE. They both dont know how this new relationship between them will work out but they're ready to do their best after all what happened. Even Donhuyn said he cannot change how he is and asks Sungho to accept him as he is and he says yes. Donhyun choosing Sungho also makes sense, he loves him because sungho needs him. It is a very codependent and dysfunctional relationship.