I think it was in ep 15 when Yong-pil and Sam-dal at separate times told his Father that they couldn't live without the other, much like he couldn't live without his wife.
Then when Sam-dal truly confessed to yong-pil how he would be the only man she would ever love for the rest of her life... which I think was in ep 14.
But ya, that whole "Love, but do it in Silence" Damn, just damn. Seeing him reading, watching, visiting her shows and she had no idea that he never gave up his love for her, until she knew.