About Eco being helped to the shower and how it diminished the trauma - he tried to ground himself before by stating Kai is his friend and wouldn't hurt him. He went over the dream and what he saw because the trauma was still lingering. Therefore the tension is still there just that he is working through it yet.
And the peanut butter is Ecos favorite thing and connection to his now old life back home. That is why it's hard on him. He isn't sure he can get anymore. It may not be as traumatic as Kai's experience but it gives him comfort when few things do in his current situation. And trust me, having something familiar or special to you, it can really help you mentally during hard times.