It really is painful seeing the two of them like that. It makes you realize just how much they actually treasure their time together, but Raku keeps putting his foot in his mouth about it all every time he's tried to talk to her since the incident at the beach. Even if you don't think you guys would work out, you don't just say something like that when a girl asks you in that way.
But, well... they're kids. They've never been in a relationship before, not really. They're awkward, and clumsy, and it's just so complicated dealing with other people's emotions on top of your own. This is just what should be expected when you're reading or watching a romantic story set in a school. Especially one with the uniquely more complicated premise of this one. But it's still hard to see, all the same.
Also, yeah... I knew Kosaki was going to injure herself saving someone else. I remember this from the anime. And then Marika is out sick (for now), so that leaves only one alternative...
And he finally mans up, and goes sprinting for Chitoge. And they finally work their shit out. Because they've both been absolute idiots talking past each other instead of actually with each other. They're still not entirely honest with each other about how they feel, but that's okay. It's just how they get along, at least for the time being. And Kosaki knows that- that's why she said, "They'll be fine," in the third-to-last panel, and smiles as she looks on at them thinking everything's back to normal.