For me this drama feels like, in a football match the team played well and when the match came to the end they got a open chance without keeper in the post. Only striker need to tap the ball into the net (striker is the writer) and he shoot it off the post and they lost a great match.
They made it with a happy ending. But still the first 30 min of the last episode sucks. Why the hell did they added a part like that in the story. It made the entire show in a bad one.
That's also possible. So, he looked her with that regret.