How? He's a victim more than scumbag. It's only now he's being a scumbag and even then that's to protect himself and not out of malice or desire.
Remember this all started with him sleeping with his sister. His sister out of sheer jealousy got mad when he interacted with other girls online and threatened him. Add the purple stalker making his life more hell by adding fuel to the fire and we have where we are now.
I'd say he's chaotic neutral:
1. found out a guildmate was his sister and slept with her anyway (lmao)
2. took a blind guess at a random guild mate that turned into him blackmail to get her to come to his house.
3. Threw his own father (who had zero to do this with) under the bus when his classmate came over to address the allegations
4. threw the teacher under the bus to get out of his very weird 5 way (which doesn't even make sense to begin with. You're known as a 4 timer and you're gonna say you wanna bang the teacher?)
5. And now, we have blackmail of the teacher after he randomly dragged her to a hotel and then forcibly took her shirt off (and sure, he thought it was a guy, but uhh... I don't randomly take off my bro's shirts unless they are in medical danger. some soda won't scald their skin lol)
There's a lot of unfortunate circumstance where he's definitely the victim
- rape threats from his sister and her generally making things worse because she can't keep her incestious relationship on the DL
- trolled constantly by the sister's friends,
- the mistunderstanding with the idol that lead to the classmate scenario
- the school letting a random college girl on a middle school campus)
- A teacher finding out a guild mate is in middle school but wanting to meet IRL anyway (lmao, right after the false allegations happened. )
But he's no angel.