If having compassion for someone who you loved for years of your life and shared a deep spiritual connection with is being a "cuck" then maybe he is. Roberto is intelligent enough to understand that the things Marky has said and done to him are the result of trauma and mental illness so he doesn't take these things personally. He looks past those things and sees the beautiful soul lurking underneath it all. He lived with and loved Marky for 3 years. There is no one in this world that understands Marky better than Roberto does.