Satoru knew how your boyfriend treats you. He knows you know. So, why don't you listen and leave him?

Fear.

Satoru doesn't know on a personal level, but he knows you're scared of your boyfriend. That's why he doesn't try to pressure you. That's why he tries to be understanding and help in any way he can.

You know Satoru would kill him if you let him. You know he would protect you from that asshole.

That's why you've now shown up on his doorstep- beaten and bloody. You tried to tell yourself it wasn't that bad. But you knew better. Satoru knew better. The door whipped open, and Satoru's face was pure anger. He grabbed your arm, and pulled you inside. His grip was soft, unlike his expression.

He sat you down and started to clean up your face- all while staying quiet. He was tryin not to kill that fucker.