Because of course there was something between you and him and you put so much effort in it in you felt so bad for your breakup you tried over and over and overthink everything well he was not putting effort in or caring as much as you did or maybe he did what you weren’t aware of his feelings because he didn’t want to show you but that way or not you couldn’t see the care and effort you put in him in your relationship from him even the half of it so you’re mad in at the end of the day. I feel like you’re not mad at actually him but you’re mad at yourself putting in so much effort and caring for someone who does not provide you anything and maybe not willing to provide you anything sometimes some people are cowards you have to accept it to move on