Judging how Yul has progressed regarding character it will be easy to assume that he will move on and get the happy ending he desserved with a new family. Blonde and sian had theirs and its simply a matter of time before yul gets his when he meets another girl.
Yes yul desserved a better ending than this but seeing him progress as a character and actually turning normal is a happy ending enough for me. Its up to us to imagine their lives if the author plans to end the story