It’s possible he tried to overpower her and potentially kill her. Seeing his potential, Tristian didn’t want to kill him, but make him pay for his attempt so she gave the scar
Tristan, while being pretty cold and distant, looks like a very easy going person and even know is very very fond of reuben... I feel like if she was that disappointed that she gave him that scar he really must've fucked up
Thats true tbf it's just hard to believe hes do something so fucked up to deserve that from what we've seen so far but your point makes sense and now I'm kinda nervous what he did
Do we know yet what he did that made Tristan give him that scar. Honestly doubt he actually deserved it but