Ch5 and the extra? Or ch3-4?
5 and the extra :(
I assume you mean what the problem between Kitagawa and Natsume was so...
Chapter 5-
Both Natsume and Kitagawa seem to be envious of Saito and Tomita, but Kitagawa moreso. While the theme of Saito/Tomita was change/acceptance, Kitagawa and Natsume are shown to be more comfortable with things staying as they are, which is why Natsume resists fully committing to a relationship with Kitagawa, and why Kitagawa says he is fine with that even though he clearly wanted more.
During the move, Natsume makes some comments about Saito/Tomita, and Kitagawa thinks that Natsume is envious of the way Tomita is being treated. When Natsume comments on how Tomita likes to be spoiled, Kitagawa says "If that's what you think..."
Kitagawa then tries to appeal to Natsume by acting more like Saito. If you recall, Tomita complained a lot about how Saito always seemed to treat him like a customer, even when they were alone. Well Kitagawa was doing the same! He was basically wearing his "business face", which is what the sound effects were communicating when he spoke to Natsume. Basically this is his way of trying to show Natsume the best side of him/his reliable side! This annoyed Natsume because he thinks that seeing "the other side" of Kitagawa is what makes their relationship special (this is why he apologized to Tomita in his head when he saw Saito's face when they were hugging). So Natsume confronts Kitagawa and tells him to stop acting like Saito (or basically, stop treating him like a customer) because he loves Kitagawa because he's Kitagawa (remember he fell in love with the blushing and awkward man). Kitagawa gets sad ("it's weird when I'm the one doing it, huh") because he doesn't know how else to appeal to Natsume.
Saito picks up on this and tells Kitagawa that he's jealous that Kitagawa can do things Saito can't. Kitagawa is confused by this because to him, Saito is like... The ideal. Saito tells him, "I can only do what I can as best as possible" which is just a long way of saying "I can only be myself". Kitagawa thinks that he only shows his shameful side to Natsume, and he wants to do better (he attempts this by following Saito's example!). Saito asks him what Natsume must think of it, and Kitagawa says that he thinks Natsume loves him, but he's not sure. Meanwhile, both Natsume and Tomita are overhearing this conversation, which Tomita tries to cover by pointing out the ramen shop.
Natsume tells Kitagawa, "if you were more like Saito, we wouldn't be the way we are now" because he wants Kitagawa to know that he fell in love with Kitagawa and all his shameful parts! He makes it more obvious when he says "No one knows this side of you" to Kitagawa, and finally Kitagawa seems to understand what Natsume was saying. When they sleep together, he thinks about how he loves seeing Kitagawa in that moment, without any sort of mask on. The events of the day soften Natsume a bit, and make him more open to deepening their relationship, which is why he makes that random offhand comment about living together! They then admit that they need to actually communicate better with it anyone else's help. So happy ending there!
For the extras-
Saito is reflecting on them getting together and how he loves the way Tomita used to laugh and gossip. But when Natsume and Kitagawa got together, Tomita stopped laughing. So Saito flirted with him to fill the hole in Tomita in hopes of being able to see the happy Tomita again.
Kitagawa and Natsume are just talking about how Natsume doesn't go to the bathroom anymore because he isn't eating as much spicy food lol.
Thank you your comment made much more sense
Can someone try to explain to me the last two chapters? I had trouble understanding and idk if i was supposed to know some kind of context or something?