The writing's a bit stilted, but I'm pretty sure it was basically Ash, back when she was Jin-Ha, was in love with her best friend, Ayoung. Jin-Ha was overly possessive, and incredibly jealous of a perceived threat taking her love away. Ayoung, all the while, was trying to get them both into this acting gig (or whatever it was) because she was genuine with her feelings about being more comfortable with Jin-Ha there.
During that scene of "forcing my feelings onto her" was kind of implying she moved too far, and was sliding her hand into her shirt. Which, of course, creeped her out. To Ayoung they were just best friends, but Jin-Ha felt they should be more. Then she goes into a spurned Incel rage, and kills her friend.
Still why did Ayoung not just tell her friend "Hey I'm trying really hard to get us a gig, but the guy is being a jerk. Sorry for avoiding you, lately, I'm just trying to convince him". Problem solved. Instead it was forced drama. If Jin-Ha didn't listen or something when Ayoung explained it would make more sense and only increase the creepy stalker factor.