Ryuuto is a certified moron. Runa explicitly spells it out to him to talk to her about what's troubling him, especially when it comes to their relationship, but the guy refuses to speak his mind about 4 times in this chapter alone! He's just hopeless, seriously...
The other guy isn't much better though. If he thinks his girlfriend is going too fast, then for crying out loud, he should just tell her that. Otherwise, I don't see the problem, I mean, sleeping with your girlfriend is hardly a week-long affair, if he had time for a double date, surely this wouldn't throw his study plans in complete disarray.
I mean.. She never voiced her intend, so he can't exactly go ahead and say he can't right now, without her actually bringing up the topic, would kinda make her sound like the h- word 😶 In a sense of her only wanting that, or being overly horny (which she most certainly seems to be) (And yes, she went obvious about it, but it looked more desperate at this point..)
He already told her he has to study for exams and he needs to focus on those right now, i dont think he needs to say any more than that, otherwise if she still has things bothering her she can speak to him, considering she apparently can lay it bare in front of her entire class.. 🤨
Also, sure it isn't "a week-long affair", but just doing it because she wants to right this instance, would honestly seem insincere, if he isn't actually in the right place/mind right now, since yeah.. it'd say his exams take priority 😐 The fact that he isn't just rushing it honestly just feel like he isn't planning to take this relationship lightly, can't say the same about her
(Though that's just how i see it, could also be completely wrong 🫡)