I think we're going to get a ugly side of her relationship so we'll hate Junsik and I'm no...

If it true, That's bad ngl... I mean the reason she happy with her life before was because of junsik, seeing the bad side of her relationship just to make us hate junsik is like giving her a slap and a stab in the chest and saying what her whole life before is just a lie.

And dang, if that happen idek anymore, if I'm her if be cursing the author, god or whatever to make one life be a whole lie..

I mean... A good story never really need to make a story where the good partner we have before to actually be a jerk and then suddenly she married with another man..

I'm fine with a story where she still ended up with her last lovers. I mean it's just make us see that "oh they still ended up together whatever they scenario they have, they just fated with each other"

What kinda story is touching and sweet to see too..

I agree, but from my perspective the author didn’t really need to make Junsik a bad guy just so she could have a relationship with another guy. They could have simply shown her realizing that she never had anyone besides him, and that’s why her relationship seemed so perfect, there was no other relationship to compare it to (friendships, family, etc.).
Her hairstyle and her clothes were things he told her were cute. I don’t see him as a controlling boyfriend; however, she didn’t really have a personality before him. All her “unluckiness” came from being passive about her own life in the pass, that's why she could change things a little bit easier this time (also she is a grown woman in a teenager body)
I don’t want him to be a bad guy, but it feels like the story is hinting that he wasn’t as perfect as he seemed.
I would totally like it if she realized that she’s the one changing, and that’s why they don’t end up together in this timeline.

My mind instantly went to thinking about possible red flags she could've missed in future junsik because of how she grew up

Exactly, its not that junsik is this adorable golden retriever. We're seeing their relation from yumi's pov so if she forgot all the bad memories (it happens often in irl controlling relationships) then we also didn't get to see them until the story shifts to what actually happened and all the moments that Yumi would rather not recall.

Relationship* mb