Volume 18 finishes up the aftermath of the Juromaru fight & the big argument over Koga. Then leads directly into Inuyasha's indiscretion with Kikyo.
After the battle with Kageromaru & Juromaru, Inuyasha looked more seriously hurt than in the anime. He was truly furious with Koga for disrespecting him and for making a play for Kagome.
He wanted so badly to prove he was better than Koga, he would do anything, even fight at half strength.
His jealousy came out in some pretty strong insults directed at Kagome. He wouldn't let Kagome treat his wounds. He called Kagome's behavior disgusting. He pushed her over the edge and then panicked when she got angry in return.
As Kagome went back to the well, Shippo told her what was obvious to him, that Inuyasha loved her but was just so insecure that he couldn't dismiss Koga as the insignificant nuisance he was.