It was true and Seolhyun knew it. She felt a twinge of jealousy every time she saw them together. In fact, Hyejeong was, at times, a bit of an over-jealous type of a girlfriend - she would randomly get jealous over Seolhyun's onscreen kissing scenes and could even go up to feeling jealous when Seolhyun played with her puppy. But it almost never went beyond those 'love fights' and all sorts of jokes, contrary to what the situation was like whenever Seolhyun got jealous. 
Though, this time it was completely out of Seolhyun's control. She frequently recalled the anxiety she felt back then, when she first got to know the girl who happened to be Hyejeong's "best friend”. 
[FlashBack] 
When Seolhyun first saw the girl almost crawling on her girlfriend, she couldn't help but feel disgruntled at how Hyejeong didn't seem to mind it and how easily she sustained the conversation. The girl was a new employee in their company, but she seemed to be really close to Hyejeong and thus, they looked completely relaxed around each other. This and many other factors kept giving rise to Seolhyun's displeasure and the jealousy she felt awoke her possessive nature. Hyejeong was her girlfriend, after all. She slowly made her way to where the two were standing and having some random chat, finding her spot right next to Hyejeong, who smiled and wrapped her arm around Seolhyun's waist to pull her close. She normally wouldn't mind these actions in public and was confident whenever she held Seolhyun's hand or hugged her randomly. 
"You know Seolhyun." Hyejeong pointed at Seolhyun with the free hand while speaking to the girl. 
"Who doesn't know the model of the year?" The girl giggled in response, and Hyejeong's lips parted in a smile. 
"This is Mi-Young, my childhood best friend. I think I had told you about her." Hyejeong now spoke to Seolhyun, introducing the girl. Seolhyun nodded with a forced smile although she didn't really even make any efforts to recall the time when Hyejeong told her about the girl who was standing before her and reaching out her hand with a smile on her face. 
"I'm honoured to meet you.” the girl said. Though, something caught Seolhyun's attention even though was not supposed to. The smile on the girl's face, her laughter, the clemency in her voice... all those were fake. A mask, to be precise. Cloaked falseness and faked emotions. She was hiding some massive feeling, akin to violent anger or jealousy maybe, similar to what Seolhyun was experiencing. Or not… it was far beyond that. Her gaze contained every single negative emotion. Loathing, hatred, disgust... so many stuff were hidden under that mask. Seolhyun could feel that those emotions were directed right at herself and, moreover, she was nearly overwhelmed by her own ability of looking through the stranger's soul.
“Seolhyun-ah..?" Hyejeong's voice snapped her out of her world of analyses. Seolhyun came to realize that the girl's hand was still frozen in the mid-air, waiting for Seolhyun to squeeze it. 
"Nice to meet you too." she said, sort of absent-mindedly and reached out her hand in return. 

It was their first confrontation, though Seolhyun’s first impression was solely negative. Not just because of Hyejeong but because of Miyoung herself. Meaning, not only that she was secretly jealous of her closeness with Hyejeong, but also the way Miyoung looked at Seolhyun… Seolhyun could literally feel she was disliked, if not hated. But, whenever she spoke about this to Hyejeong, the latter would just prove her wrong by saying Miyoung actually really liked her and respected her acting/singing/dancing talents. It never made Seolhyun doubt all those were just made-up excuses, however. She wondered, how couldn’t Hyejeong see it? The way Miyoung looked at her was not the same way she looked at others. 
But, even that wasn’t everything. As stated before, Hyejeong wasn’t really all frightened to show off her relationship with Seolhyun; though, she was professional at hiding it under the ‘Best Friends Forever’ catchword, so no one really ever got suspicious of them being in more-than-friendship kind of terms. But it was a little different when they were around Miyoung; Hyejeong was over-obvious. It felt like she wasn’t trying to hide their relationship, and acted directly like her usual self, instead of hiding behind that friend-like concept. 
“Ah, don’t worry.” she smiled when Seolhyun actually asked her about the reason of her obviousness and straightforwardness. She explained that she was sure of the way Miyoung would never judge them. “I forgot to tell you… Miyoung herself had a girlfriend.” 
“She what?” Seolhyun froze. Now she indeed had a reason to be frightened by their closeness. 
“… dated a girl? Why does that surprise you?” 
‘Why? Are you kidding me?’ Seolhyun panicked inside. “Did she tell you about the reason over their break-up?” she asked, straightforwardly. 
“How do you know they broke up?” Hyejeong raised her brows for a split second and then dropped them back. 
“You used the past tense.” Seolhyun explained. In fact, Hyejeong only told it a few seconds ago: but it was more than enough for Seolhyun to build up an image of a random girl, who happened to be Miyoung’s ex-girlfriend, how Miyoung fell in love with Hyejeong, how she broke up with her girlfriend, how she started flirting with Hyejeong - in short, Seolhyun made up a whole plot as though she was writing it for a movie. 
“Oh, right.” Hyejeong laughed at her clumsiness. “Well, she told they broke up because her girlfriend didn’t love her as much as she loved herself. Or something like that.” 
It was then that Seolhyun felt terribly troubled. It went beyond the usual feelings she received normally. The jealousy she felt transformed into fear; fear of losing her partner. And every time she confronted Miyoung, an unpleasant feeling caused by the belief that she was a threat to Seolhyun’s relationship would not leave. 
Hyejeong, meanwhile was still the same caring, loving and sweet girlfriend that she used to be, and there was nothing different in her attitude towards Seolhyun. She never skipped an opportunity to call or message her during work, to hug her nearly everywhere and to kiss her privately, she never forgot to cuddle with her all night long, whispering sweet nothings in the mornings and genuinely caring about her even though she herself was exhausted from work. And that gave Seolhyun enough confidence that she would never be left. 
But still, the question of why was she that much disliked by Miyoung got stuck in her head and she wasn’t able to get rid of it without getting a proper explanation. The only reasonable answer was that Miyoung was just jealous of Hyejeong, according to Seolhyun. And as Hyejeong’s girlfriend, she had to protect what was hers. And if needed, she was ready to fight against Hyejeong's best friend who presumably fancied her.