IMHO, I am relieved that Nabi finally made a decision and took a chance on Jae Eun. I am a believer in going with your heart no matter how chaotic or potentially hurtful, loving until all the love is gone; rather than going for the safe choice. Sorry, I was never a fan of the “safe choice”.
It was obvious from the start, that Nabi was attracted to Jae Eun ( more than with Do Hyeok) but was defending her heart from potential hurt. Jae Eun on the other hand wanted to play the field until he met someone who disconcerted him. So now they are trying out dating and whatever the outcome, they, at least, tried it.
Just one thing that bothered me, is the part where Jae Eun said he “fell in love” with a girl in the museum (Nabi). Was he saying it was love at first sight? I find this inconsistent with how he was acting up with other girls even after he was introduced to Nabi. But anyway, it could have been him not realizing the extent of his feelings yet and still wanting to play around.