>>/4103/
Interesting quotes that I am going to read too much into
> the following will be the last message that will come out of my mouth or mind that holds any pity or remorse for you.
I wonder if this is supposed to mean that he wants to move on completely (emphasize on "last message") or if he wants no longer to hold back (emphasize on no more "pity or remorse"). 
> i know that this relationship with seth is the best you've had in a while
Which implies that she's had relationships before that weren't all that good.
> seth can go to jail for at least fucking 20 YEARS.
As others have pointed out: statutory rape or child porn. Lazy also says later that they plan to "wait it out" but "it'll be still be illegal", which could be what this is referring to.
> i know that your words from before was just out of spite but now it's evidence. if anybody uncovers such information about you and him, your relationship will be for forfeit.
Could be that these "words out of spite" refers to Bonbi accusing Seth of emotional manipulation & abuse or something else said in private.
> even our relationship as close friends is not healthy
Why would he say that? They're of a similar age and seemed to get along until recently. Unless, this is about Bon's continued refusal to go outside and her dependence on other people.
> cosplay is not healthy
Also a form of escapism? Cosplay seemed to be one of the few things that made her happy.
> ...and your desires from [for?] him are not healthy.
She horny.
> however this heartbreak will heal but the trauma will last. no of just seth but all of this. the doxxing, the threats, the hate, will follow you unless you yourself heal
Again seems to show that Bonbi prefers escapism to dealing with reality. She tries to ignore all the "haters" and problems in her life without every confronting them.
> i can deal with knowing that you're going out with not a monster, not a mastermind, not a manipulator. but someone who can destroy all the bonds you had with so many great people
I'm going to assume that the first half of this sentence is primarily there to concede something to Bonbi. I would guess she worked very hard in private messages to convince (former) friends, that anonce is really a good guy who's just misunderstood.