Remember the song YoonA sang at her birthday party in 2017?
"Hero" by Okdal.
You don't know how nice a person you are
It is only me who knows
Though others don't know you yet
You're just smiling without saying
Like that, you're warm, you're the hero of only mine
When you feel lonely and sad
I will hold your hand tight
"All The Time We Spent Together"
I’m always like this Rather than words, I just put on an awkward smile
In case I’ll make you sad, I just smile
Just like WTWB, she's basically saying the same things he said in his 6th Album using the same words. She's answering him and reassuring him at the same time.
WTWB was the culmination of all, but not necessarily the end.
When you think about YoonA's behaviour and see how she behaves, it's actually hilarious and paradoxical.
1) Just about as ALH was starting to play in the car, she went hysterical and told her Chinese teacher/translator to shush.
2) When Heechul made a pun on his name, she was startled and stunned, she couldn't react in any way but with a forced smile/laugh until she regained herself and launched her hammer attack.
3) When Sooyoung mentioned Strong Heart, she didn't say anything.
She puts so much effort and thought into picking these songs, making it obvious to all, but then she doesn't want anyone highlighting that very fact, and gets mad/angry if someone alludes to him or makes a direct or indirect reference to him lol.
At the very least, she was/is having an internal conflict.
Even now by singing WTWB at her FM's, by doing so she's automatically thinking of him, because there's a part of her that wants to.