Jeremy should have left Noah alone? Absolutely not.
Does this make Noah's suicide Jeremy's fault? Absolutely not.
Both things can be true at same time. Jeremy should have not chosen to go stuff his nose with drugs in a party instead of staying with his clearly depressed brother who had expressed needing him at that moment.
This still doesnt mean Jeremy has any blame in Noah killing himself. Noah needed a whole bunch of things he didnt have access to at the Wilshire's home. Even though depression doesnt have a clear set of causes, there is no way to ignore how much the toxic environment must have contributed to Noah's mental illness. Not to mention Mathilda proceeding to refuse to get Noah the help he needed, both in the form of therapy and medication.
As OP said, If Noah hadnt killed himself that night, he would have the first chance he got. At some point, someone was going to make the mistake of leaving him alone and, without proper treatment to his depression, Noah would have taken this chance to kill himself, leading the person who left him alone to feel guilty forever. With the way things were going, It was inevitavitable.
Jeremy made a stupid choice, like stupid teenagers tend to do, and it was indeed a bit selfish. None of this will change the fact that a clearly depressed person should have never been trusted in the hands of an 18 years old struggling with addiction. From what Jeremy describes, Noah should have probably been in a psych ward with how bad his depression was at that point. The whole situation was screaming: this is gonna end badly from the getgo.
It end badly, to the surprise of zero people.
Bryson has way more fault in this for hooking his own brother on drugs. Above all, the person who should be taking all the blame here is Mathilda. Her neglect would inevitably lead to Noah's death. The only thing that could have changed Noah's destiny was If this absolute piece of shit of mother could take her head out of her ass for a total of five seconds and allow her son the proper treatment. As long as Mathilda continued to deny Noah the proper treatment, Noah's destiny was sealed.
It is shameful that Mathilda blames Jeremy while refusing to acknowledge she is the one who failed as a mother. And she failed not only Noah, but all of her children. All of them were in desperate need of help from their family and mainly from their mom. What they got was someone more worried about PR than with their well being.
Noah was a kid and he needed his mother. Jeremy too. They were both kids who needed their mom to step up and help them. She never did.
I really hope somebody tells this to Mathilda in TBC, she deserves to hear It. Blaming Jeremy is easy. Accepting she failed as a mother fundamentally probably isnt.