CHOI SIWON is a successful football player in the United States. He lives in New York with his wife YOONA who is a fashion magazine editor. They have a son named Henry. Also living with them is Siwon’s mother Ms. Choi.

LEE DONGHAE is an orphan who is to marry his closest childhood friend JESSICA - the two have been raised by Jessica’s fun-loving father Mr. Jung a.k.a Sam.

Siwon encounters Donghae moments before he is to marry Jessica. Coincidentally, it is also Siwon and Yoona’s fifth wedding anniversary. Although Siwon and Donghae are strangers, they connect instantly. The two part ways and Siwon bids Donghae goodbye - Donghae tells him that they should never say goodbye because they may meet again someday. Moments after they part ways, Siwon is hit by a car and injures his leg and as a result is no longer able to play football.

Four years pass after Siwon and Donghae met one another. Siwon is now extremely bitter - firstly because of his inability to play football and secondly because Yoona is very successful in her career making Siwon look inferior to her.

Donghae is in a similar situation - he has found that he is infertile and generally does not feel any love towards Jessica because he believes she is quite selfish.

The two couples meet and quickly become friends. Jessica invites the Chois to Sam's party. Here, Yoona and Jessica go off and dance together, much to their partner's irritation. Also, Sam and Ms. Choi show blatant signs of falling for one another.

The next day, Siwon and Donghae witness Sam and Ms. Choi embracing one another. When they confront them about it, Sam and Ms. Choi explain that they are both in the same situation (i.e. they have both lost their original partners) so have decided to come together to help one another. Siwon and Donghae notice each other's marriages failing miserably - they decide that as friends, they need to help one another in saving their marriages (taking into account what Sam and Ms. Choi said to them).

They meet everyday for a coffee and discuss their faults as well as Yoona and Jessica’s. Eventually though, Siwon and Donghae decide to take a break from saving their marriages and decide to spend some quality time together. They find themselves being drawn to one another.They blissfully unaware of what the forces of love have in store for them. What starts as a pleasant friendship develops into something deeper which soon throws the relations between the two couples in turmoil.

On their wedding anniversaries, they decide to organize a meal for their partners. After the meal, both couples have an argument. Siwon gets angry when he thinks Yoona accepted a promotion to shift to London (in fact she was going to tell him that she refused it). Jessica gets angry at Donghae when Donghae doesn't get any feeling on bed and he accuses her of being selfish and not understanding his needs.

Donghae arrives at the station and finds Siwon there. The two argue and Siwon eventually admits that he has fallen in love with Donghae...

don't say goodbye...

goodbye kills the hope of meeting again...

and who knows?

we may meet again...