I think he's apologizing for all the grief he's caused his dad, friends and even those he beat up. It's also possible that he's apologizing for not being "good enough", which would also explain his waking behavior. In his frustration over not being "good enough", he lashes out at anyone and everyone. I also think his attempts at finding a job were spurred on by the girl who returned his clothes, indicating that she dumped him. His efforts, then, were for nothing and he reverted to his violent tendencies.
Ah, got it got it. Thank you~
I just reread the chapter and (since it is pretty confusing to me with all the jumping between times) I thought he was apologizing to his underclassman for forcing him but it makes more sense that he was apologizing to everyone else. I mean I think the one he hurt the most is the guy he's still hurting to this day? I don't even know if the brunette thinks of him as more than an object right now.. This really sucks...
What is sakata apologizing for in chapter 3??