The app literally told Yeong to kiss Dobin early on. Even though he did not possess the app. This app is unpredictable and maybe it's objective was always to pull him (Dobin) in to this. We've seen what it can do and if it wanted Dobin, it was going to get him. If one of them hadn't given him the app voluntarily, the app eventually, probably, would have orchestrated a situation that would require one of them too. This is app is playing games and now it has everyone it wants to play in the palm of its hands.
Feel to comment corrections or ideas, let's see what we can brainstorm.
(This is the song playing in-story; it is by Utada Hikaru, these are the Romanji/English lyrics)
http://www.megchan.com/lyrics/index.php?title=Utada_Hikaru/Dareka_no_Negai_ga_Kanau_Koro
誰かの願いが叶うころ
Dareka no Negai ga Kanau Koro
(When Someone's Wish Comes True)
chiisa na koto de daiji na mono ushinatta
tsumetai yubiwa ga watashi ni hikattemiseta
"ima sae areba ii" to itta kedo sou ja nakatta
anata e tsuzuku doa ga oto mo naku kieta
------------------------
I've lost something important over something small
The cold ring showed its glimmer to me
I said, "All I need is today," but that wasn't the case
The door leading to you was gone without a sound
anata no shiawase negau hodo wagamama ga fueteku yo
soredemo anata wo hikitometai itsu datte sou
dareka no negai ga kanau koro ano ko ga naiteru yo
sono mama tobira no oto wa naranai
------------------------
The more I wish for your happiness, the more selfish I become
But still, I want to hold onto you - that never changed
By the time someone's wish comes true, some child will be crying
And still, the door won't make a sound
minna ni hitsuyou to sareru kimi wo iyaseru tatta hitori ni
naritakute sukoshi gaman shi sugita na
------------------------
As needed you are by everyone, the only one who could heal you
I wanted to become that person, and I realized I endured a little too much
jibun no shiawase negau koto wagamama dewa nai desho
sore nara anata wo dakiyosetai dekiru dake gyutto
watashi no namida ga kawaku koro ano ko ga naiteru yo
kono mama bokura no jimen wa kawakanai
------------------------
To wish for one's own happiness - is that selfish?
If that's true, I want hold you tight - as tight as I can
By the time my tears dry up, some child will be crying
Things unchanged, the ground under us won't dry
anata no shiawase negau hodo wagamama ga fueteku yo
anata wa watashi wo hikitometai itsu datte sou
dareka no negai ga kanau koro ano ko ga naiteru yo
minna no negai wa douji ni wa kanawanai
------------------------
The more I wish for your happiness, the more selfish I become
But you won't hold onto me - that never changed
By the time someone's wish comes true, some child will be crying
Everyone's wishes can't be granted all at once
chiisa na chikyuu ga mawaru hodo yasashisa ga mi ni tsuku yo
mou ichidido anata wo dakishimetai dekiru dake sutto
------------------------
The more this small Earth spins, the more kindness binds to me
One more time, I want to hold onto you tight - as soft as I can
Poor lil Donut ಥ‿ಥ