Being in love with someone and planning to get married is a big thing you know and that ml sister I mean I know she went through some sh*t and got traumatised but dude you were going to marry him and spend the rest of your life with him you were his fiance his lover and when you both got into an accident and he pretty much got severe injury cause he was protecting you and how do you repay him by just calling it quit by saying that you cant handle it and went to vacation or whatever to forget about everything I guess .. like imagine being married to someone like that - no thank you ... And we have the ml who took care of him for 2 years straight, been there for him through all the weekly memory lost cycle and took care of him despite the fact that when the ml loses his memory again he have go through the pain of explaining "your unrequited love" hyung about his sister and his illness and its not like its only the mc who is stuck in loop but the ml too cause he has to be gentle and calm with his words so that it won't affect the mc mental health so yeah many may not agree with me but despite all I will choose the ml over the sister.