
Reading comprehension is chasing you, but you're faster.
Questioning why your manwhore, cheating, homophobic and asshole friend, whom you've known for your entire life (so, 20+ years) is now in a relationship with a man, and struggling to understand it's serious, is not homophobic.
She's not being homophobic.
She's not invalidating his sexuality.
Her friend of more than two decades did a 180° and she can't believe it. She even asks Jaehyuk to consider Garam's feelings if he just wants to play with him
I'm up to date with the raws, and she hasn't made an appearance. She WILL be an asshole if she rejects his sexuality in the future, but she's not homophobic in this chapter. You just:
a) Can't read
b) Hate women

As always, the BL community just loves to hate on women. A woman voices her valid concerns and she's a bitch, and it's most likely other women saying it. And yeah, I'm a man and I can point this out because I see it way too often.
1) Yes, she's been his confidant and she knew he liked a "Han Garam", but the way Jaehyuk talked about him sounded more like he was frustrated with his own feelings and wanted to date this Garam just for his feelings to go away and resume being a womanizer. He himself told HER that he might start dating and then get tired, he told his friends that he didn't see the relationship lasting long AFTER they were living together at that house. Yes he's definitely changed and is madly in love, but he said those things.
2) He called Garam ugly, but he was most likely referring to Garam's aesthetic, especially when he tried to gift Garam "nice clothes", like what he's currently wearing. Still, he was ambiguous and she just ASKED him "didn't you say he was ugly." Which doesn't even HINT that she thinks that's the case, she's just quoting him.
It seems like a woman doesn't even have to be a love interest for people to hate her when they're reading BL

Like, she even seems concerned for Garam. She grew up with Jaehyuk, she likely has known him for more than two decades and he was ALWAYS an asshole and a womanizer, so she thinks he'll likely do the same, just to a guy this time, and even asks him to consider how hurt Garam could be if that ever happens.
At no point does she seem homophobic. I could stretch and say that "I don't want to hear about it, especially your gay love affair" is a homophobic statement, but it reads more like she can't believe her asshole friend became this cutesy, lovey-dovey person, especially for another man as he never showed any indication of liking men.
Dislike this all you want, you're just misogynistic.
People, we should focus on the cuteness of the chapter. We'll get to know what happened with his ex, but the main problem right now is Jaehyuk's mother, and not because she discovered the relationship...