This is wetsand not drysand. Tj was already working to be in the gang before David even got to Ian. Tj confirms he wanted to be on top for his legacy not because he wanted a better life for both, he just wanted the higher power and it's obvious the reason he got mad for Ian using the David Kim name was because Ian knew at that time tj liked him, he felt betrayal Ian used that name knowing tj likes him. It's also a sense of envy tj has on David.
Remember Jason tell tj it better to do a boxing career than killing Jang and tj refused, he wanted the gang instead. He had a perfect opportunity to get a better life that way and he didn't. Also tj didn't get Ian sober, Ian did on his own after hearing that his mom died in jail and didn't want be like her.
All these horrible things happen because tj was selfish in what he desired. When he killed Jang to be a full member he unknowingly set Jamie into motion. Now that tj found Jamie brother who he could use for leverage but instead set him away he indirectly got the brother killed by other gang. Which we have yet to see Jamie retaliate. Tj [indirect] actions is what caused things.
David only ruin Ian but it did not cause all these things. You think his death would cause an uproar but it didn't it shows that his story only caused Ian suffering mentally and emotionally but had no direct/indirect connection to tj relationship with Ian
i get it now why tj lost his temper and screamed at ian when he saw david kim’s name. while he was not the one who killed david (so no guilt triggered), he loathed david bc david was the one who started everything. ian and tj (& jamie too) was not yet working under jason back then, david saw ian and tricked him into becoming a junkie and abuse him. to gain power and get ian sober, tj finally accepted jason’s offer to work for him, that was the first time tj killed someone and his 1st step towards gang life, (it was ian’s 1st to kill david later). if it was not because of david, their life would not be gang related, tj could still be a boxer and ian could find something he’s interested in. the reason tj wanted to earn sm money was to secure a better life for them no matter how dirty the work he eventually has to do, he kept going deeper and deeper but unfortunately that well-off life was not what ian wanted. the mansion in cali, even chiwoon knows ian would not like it so there’s no way tj doesn’t know, at one chapter when he’s at the hotel drinking alone looking out the window, he asked himself what was all he had done for. but tj can’t give ian a peaceful life yet so he’s trying to make up for it with material stuffs. for me tj selling the mansion is a good sign whether tj genuinely let go of ian or it’s a new beginning for them (ig i can say this after chapter 80 )