Fighting an illness and experiencing recovery like that is no joke. Saying "we can get through this together" isn't gonna make the process turn into a flowery path. Its a dilapidating experience that breaks down physical, emotional, mental and economical aspects of the people involved. It hurts badly that Haebeom's dad had to experience that but it was the greatest act of love for him to let go of Hyeonji- maybe he wasn't thinking of it that way at that time but in hindsight, it was the best. And who's to say Hyeonji avoids dying if she had gone with him? Atleast Haebeom had his mom and a whole village to take care of him, and he grew up so well. The dad is here now and making amends, they can choose to settle their matter now without regrets.