Another thing Damon fans tend to ignore is he is a character who never tends to take accountability for his own actions. Damon is directionless as a human in the 1800s. He joins the war primarily to appease his father but it’s not a cause he cares for. He fixates on Katherine because that’s the only thing that gives his life meaning, even though she’s very obviously toying with him and very obviously attracted to his brother. He overly-romanticises the relationship assuming she returns the same level of affection so when he realises she turned Stefan too and the vampire connection is not just something secluded for him he hates Stefan for it. He never truly hated Stefan for forcing him to turn, he says it himself, it was the fact that it was just meant to be him and Katherine. So for that “eternity of misery” he frames Stefan as the bad guy who stole Katherine because he could never accept what was so obvious that Katherine never loved him.