@Alacran
Of course she was always gonna say no, but she still has to properly answer...
I've read this chapter couple of times, and every time I get to the end I get very annoyed with Yusa. You don't have to give that dirtbag a proper answer to his confession. You don't have to answer him at all. He doesn't deserve "closure" (oh, how I hate that term). He didn't consider how his confession would adversely affect you, your boyfriend, or your relationship with your boyfriend, now did he? Argh! It just annoys me to no end how she can be more considerate of that jerk than her own boyfriend.
And what kind of faithful girlfriend is Yusa when she can't immediately say "No" to a confession from another guy? What horseshit is this? Will this scenario repeat itself every time some other guy confesses to her? When she and Kaede are married, is she gonna hesitate when other men ask her to spend the night with them? The best thing Kaede could do to preserve his own sanity is let that dirtbag have her and accept Yae's confession. She, for one, would immediately have turned that dirtbag down, no quesitons asked.