On TV, Abraham’s death took a huge toll on Eugene, knocking him back down to past levels of courage and determination, which is arguably the inciting factor for the character’s new differences.
In the comic books, Eugene uses Abraham’s death as a motivational launchpad and becomes an ammunition-crafting whiz, only temporarily showing regrets about having masterminded the bullet-making operation.
Meanwhile, TV Eugene is cowering before anything bad or good can happen, and it takes him no time at all to seemingly forget everything that made his time with Rick & Co. worthwhile.
When he’s eventually taken hostage by Negan, his time in the Sanctuary is the exact opposite of what we saw on TV; he not only insults Negan and refuses to work with the Saviors, but he also promotes Rick’s vision for a peaceful world from the word “go.”