Sunwoo sees Hyunseo smiling, thinking it was to wish him good luck with the real Heeji, but it’s pretty implied Hyunseo took the clone to have sex with her and the smile was about that instead.
When the MC’s teacher does a home visit to his house, she immediately falls for the FMC, so she begins flirting with her and trying to seduce her.
When the MC leaves the room, the teacher goes to kiss the FMC and they start having sex. While this is happening, the FMC thinks that she might fall into becoming a lesbian, but then the MC walks in on them and the chapter ends.
The teacher is never seen again after this and the FMC doesn’t question her sexuality again either.