I get the plot twist and its relation to the three metaphors: old/new sneakers, couple ring, and Jeju tickets. However, it needs an explanation for the ending of the Jang Hyuk and Da Eun couple as both are having affair. They live in the same house and Da Eun is carrying his baby. How they would settle that out tho?
Also, they will have another problem when both Bo Young and Lee Jang Hyuk find out that they are just a rebound.