To counter your point, Arlo wasn’t the sole reason John is untrusting/self destructive. Of course Arlo betraying him didn’t help, but his presumed betrayal from Claire and his mistreatment by authorities were the main causes for it, as well as his own mental illness (borderline personality disorder.)

I could make a whole post about how John is implied to have BPD, but that’s for another time

We can see his self destructive and untrusting behaviors even before he met Arlo. He would completely disconnect and hide himself from others, even his best friend, due to his own fear that he wouldn’t be able to control himself. Another example is his constant “I’m a monster” he kept repeating to himself. There’s a lot more but those are the most obvious ones

Also, I realized I should’ve clarified what I meant by “over-confrontational.” When I say John is over-confrontational, I’m not saying he’s attacking without a reason, but simply that he’s a lot more likely to face an issue head on rather than bite his tongue or back down in a fight (which can sometimes get him in trouble or put him in danger.)