Am I forgetting something? Why was mc punching walls
Because he's frustrated, imagine being left by the people you love the most, then you reunite again, but how do you react? Why they left? Why doing it? What should you do now? How to proceed? It's not easy to just take some emotions and store then in a box. He was just venting to what to do, and Mebaru kissed him cuz she knows that would make him feel better, cuz he likes her. So, it's only frustration and venting, hurting himself to stop the bad feeling in his guts, probably.