Shinobu's final words to Seishirou connect to what Araragi tells Hanekawa at the end of Neko Shiro after running to help her with the Tiger; their dialogs were parallels and he used words similar to Shinobu's, saying he appreciates how Hanekawa feels, but there's someone else now that he wants to be together much more.
Now let's talk a bit about Gaen here, because many explanations were left out of the anime, but were in the novels:
-First off, why did Gaen ask for Kanbaru's help? In the book, Araragi has many thoughts after seeing her argument with Shinobu and at the end of it he concludes that Gaen needing Kanbaru's arm was a lie. She just knew that because of her personality and her understanding of being in the same position as the First, she would talk to Shinobu like that;
-Also, in the anime, at the end there, after Araragi uses Meme's talisman on Seishirou, she seems genuinely surprised, but in the novel that is not true at all, she just has her usual smug air. Araragi thinks to himself that she is lying again and is not surprised in the least (I'd even compare this scene to the one in the Goblet of Fire where the "Dumbledore asked calmly" was changed to him shouting desperately at Harry in the movies xD)
-Like we already know from Koimonogatari, when she manipulated Kaiki and gave him money to conclude the job of exorcising Nadeko, Gaen is extremely calculating and manipulative. She maintains a facade, but things play out the exact way she has planned. Last episode I said she told Araragi she hired Sode so he could help them fight the First in case things went south, but now we know that's not true, and he was there just to clean up and take the armor. Araragi mentions in the novel how Episode kind of disappeared after the duel;
Well, time for Koyomimonogatari now, as we approach the end!