To be fair to Asher I don't think he realised how fragile Silver is. Yeah, he's strong and brave but he's still fragile. Asher didn't go through what he did, not in the same way, and he thinks he understands but he doesn't, no one does. He's done s lot for Silver in those few days he's known him but he still doesn't understand him like River does, because he doesn't know him like River does and although in many ways Asher has done more for him than River has recently, when he's sick and confused River is who Silver really wants, who he reaches out to, because River has always been there and River understands.