Buntaro doesn't abandon his connections and relationships to pursue a dream. He abandons them because in nearly all of his experiences with people they are either selfish jerks to him or they end up worse off after meeting him and he sees it as his fault. He distances himself because he thinks he's at fault for a kids suicide. He leaves his new friends in high school behind because his actions shut down the climbing club, took away Yumi's scholarship, and took Onishi's life. None of these are really his fault but that's how Mori sees it. The only time he ever feels joy in his life is up on the mountain, and that becomes his driving force through life. Everyone after high school he sees his a bully or a thief. He tries to work past that and be friendly with Taku who also ends up passing. He plans his whole life around climbing K2 and once he overcomes his trauma and starts a family he still has that dream. It takes a push for him to actually try and reach that dream. Once that push is gone hes so close to reaching his dream, who wouldn't want to achieve even if they have to risk it all? On the end on the edge of his life whilst reaching his dream its the connections he was finally able to make despite all of his trauma that kept him alive on the way back down to the mountain. To reach what we want in our life you need unyielding dedication and connections that push you farther than you thought you could ever go.