While I did enjoy the positive aspects of their relationship, he lied to her. In the episode where J’onn’s father was making people angry because of his powers, she expressed her feelings towards him which perfectly describes how and why they weren’t good together. And I will be honest, I’m a Supercorp shipper, and while they had a falling out, they managed to get past it and had conversations. They should’ve been endgame because they compliment each other well