Secret Campus

There’s something on Taejoon’s mind. He’s been dating Yeona long enough that they know each other’s bodies inside and out, but something's missing. Something that’ll add a thrill to their perfect relationship: a threesome. However, when he finally brings the topic up, Yeona threatens to break up with him. That only piques his interest in the forbidden topic, and he soon comes up with a plan to go through with his ultimate fantasy.

(Source: Lezhin X)