In paradise, both of them confirmed to each other that they are each other's final pick.
But then, the player Gwanhee strikes again and become wishy-washy when they came back to inferno.
Remember the fake news scene with Gwanhee, Habin, and Minkyu? Those guys really didn't know. They cannot read Hyeseon's inner thoughts that's why they just assumed that she's into Won-ik. This rattled Gwanhee and makes him more intrigue about Hyeseon.
Part of the reason is, Hajeong shows her desperation to be with him to the point that she back-pedaled about her stance of him being rude during that 33℅- this-and-that scene. She went back to him and apologized, and that's a big turn off.
When Hyeseon picked Wonik for a paradise date, Gwanhee picked Minji to get back to her. See? From this point on, SHE'S IN CONTROL. She has influenced Gwanhee's reactions.
Hyeseon truly wanted Gwanhee to pick MJ. She was not joking during that scene when she told him to pick MJ.
But why? Why Hyeseon wanted Gwanhee to bring Minji to paradise?
It's because she wanted to confirm his true feelings for her. If his feelings for her are still strong after Minji, then that's good but if he'll have second thoughts, then that is a sign she needs to show her card & check 1 last time if both of them are really into each other.
4.) By choosing herself above anything else but also staying true to her feelings.
When Gwanhee and MJ came back from paradise, Hyeseon heard and saw everything. That's when she pulled and showed her card by winning the girls final game and bringing Gwanhee to paradise.
Hyeseon, although she wanted to become GW's endgame, doesn't want to sacrifice her self-worth just for a guy. And here's how she used the Skinners reinforcement theory and get the response and reaction she wanted to see from Gwanhee.
She told him again to pick MJ if he still hesitates. By doing this, he forced GW to imagine a future without her. And this has seriously rattled Gwanhee that he immediately reassured her that she is his final pick.
But then, later on, during the bonfire scene, Hyeseon saw Gwanhee and MJ's interactions. She was pretty pissed off when he told the group that he hasn't decided yet who to pick. It contradicted to what he's been telling her since paradise date.
When asked if there's a guy that makes her heart flutter during their week-long stay in the island, she answered NONE. At this point she's done with him and doesn't care what will happen next.
Hyeseon, being a bubby person, not sharing her inner thoughts, but broke down crying in their last night in the island had woken up Gwanhee's PATHETIC SELF-ABSORBED brain.