He felt so angry. All the negative feelings someone could experience, anger, pain, betrayal, sadness had all gathered inside of him at this moment and gave him the final push to act. Those were his driving power and he felt like a black aura had surrounded his body.
Luke didn't know what he had created. Alex was never like that, he never felt so negatively. He always believed that things could get better. That there would be always a way but he had taken that strength away from him and now his only source of power was his displeasure, his agony.
So driven by all of these monsters inside him he launched forward and jumped on him. Luke surprised by the sudden attack fell to the ground with Alex landing on top of him. He was crying, unable to breathe properly while his fists landed angrily everywhere, filled with hate.