First half of the story presents MC interaction with her ex-fiance and ML prior to engagement. We get to see the ex mix feelings for what he is about to do, ML's secret love for MC and MC preoccupied with her works, school and noticing the ex's "cold feet".

There's a lot of build up until we reach the middle- the engagement. The ex came to the party with MC's "rival". MC confronted them and was really heart broken. ML stepped up and proposed to be the groom instead and MC accepted. The ex immediately went MIA. MC's rival immediately regretted her action as she realized the consequences of her action (I have no words how she would be dumb enough to realize it late that she is essentially acting like a mistress and destroying a couple)

By the last half of the story, we get to see MC and ML slowly warming up with each other. We get to see the ex regretting his decision and explanation to his action.

Apparently he had a dear aunt who log out of life. Before that, he had a conversation with her and she was talking about karma and the "little kid of the Su family". Upon confirmation, he thought that it was referring to MC and that she said something to her aunt to act like this. He and MC were around 17 at this time.

I have no idea why he immediately thought that his old aunt log off was due to the 17 year old MC but he did. Somehow he thought of taking revenge by becoming her boyfriend for how many years and then dumping her during the engagement party so she can feel what his aunt felt like...

Turns out, it wasn't even MC that talk to his aunt but MC's littler sister. He didn't realize as she rarely talks.

As to why the aunt logged off? Because she poisoned her high school bully and the little sister heard it. The little sister denounced her. Overcome with the fear of the consequences, the aunt logged off.

All of this just revealed late in the chapter after the ex confronted the two sisters. How come he never thought of this or asking the two for confirmation is beyond my mental capacity.

The end shows MC moving on with her life with ML, no longer caring about the ex in consideration that he is ML's half brother.

Finally, we have an extra chapter of MC and ML having a kid.

Of course, it wouldn't be an ex regret story without the ex unable to move on from the past and still loves MC.

Somehow on the day he came back to the country, he bonded with the kid which surprises everyone.

HE.