Wow! Perfect story of manipulation and betrayal. Totally clear that you can be manipulated when it comes to assumption of trusting or liking someone you don't know fully. You really have to look in the mirror and ask yourself to get a clear mind of making the right choices and decisions with your life. She just realized that when she walked away from him in prison, lesson learned.
I really liked this kind of movies - suspense thriller. I was rooting for her and her friends at the yacht to save her or she would have been killed by Seong Yeol. At first, I was putting my trust on him too and thinking how he and her would get away with the murder or scheme after. Greed and revenge usually do not have good outcome. They will eat you up.