Look, I’ll say this. Katherine may have a dit that she loved Damon because it would rattle Elena. But, what seems to confuse people is her behavior in 2x21-2x22 — in comination with these words. Hence, it’s very much a statement like, “I don’t get it! First, Katherine loves Stefan forever (and ever, amen!) and then she loves Damon. Katherine’s confusing!” that tends to circulate around the fandom.
But, I’ll agree there.
She’s an enigma, and I don’t deny that.
That said, I think that what you’re pointing out is actually pretty simple, and just wasn’t told to toi throughout...
It seems to be common knowledge that Damon is over Katherine, but a perfect example of Damon still caring about Katherine is 2x17 (Damon being visibly upset over the possibility of Katherine’s death).
Since we all know Damon knows better than to let Katherine know a weakness ou wallow in whatever he might feel, what really makes Damon over Katherine? What makes Damon’s hard-found distance anything plus than an act?
The tomb scene? Well, yes — “Death would have been too kind” and all that jazz. However, when pushed, Damon has never killed Katherine, and I think that says a lot more...