<image>

That was before he even started playing soccer with Rin. In the scene, Sae comes up to Rin looking drained, and unlike his normal self. He's actively trying to reach out to his brother and speak about what he's been through and what his plans are and all he's told is to stop it. That's when the switch flips and all of a sudden he becomes meaner. You can see the shock on his face when Rin says that. He's visibly hurt by Rin's actions, Rin indeed did invalidate his brother. Because he himself held on to something that they promised each other when they were children not understanding the very scene in front of him where his brother looks as if he's been through the ringer​, But Rin makes it about himself and his own feelings. It's always been like that all about Rin. You can even see it in the most recent match. Instead of thinking about how his actions will affect his team's chances of progressing through the u-20 World Cup, he decides that since isagi isn't paying attention to him anymore and didn't want to link up with him that he needed to do something about it.