Katherine did not love Damon. She made that obvious in so many nasty little ways that should have niggled at Damon and prevented him from giving himself over to her completely. But he was blind to it all. It wasn’t real… and on some level he knew that. But he didn’t care.
With Elena the opposite has always been true. He wants it to be real, perhaps because he is so conscious of the fact that he lived a lie for several lifetimes waiting for a woman who only ever seemed to want him some of the time. But I think the dichotomy was not absolute in those early stages. Damon, as he puts it in season 2, was a work in progress. Part of him wanted it to be real with Elena. Another part of him would have taken anything he could get and filled in the blanks with his over-active, lovelorn imagination.
When he made his speech to not-really-Elena on the porch in 122 he talked of being saved by her and was rewarded by a kiss. He still believed – or wanted to believe – that it always comes down to the love of a woman. The truth is that it doesn’t. And that’s what he’s come to know and understand. Because Elena did not give him the immediate emotional gratification he was seeking, he was forced to take a step back, adjust, decide what it was she really meant to him, beyond that overall tingly, breathless feeling of being in love. And he decided that her friendship was enough. That was the turning point for Damon. Because if ‘just friends’ with the girl of your dreams is enough, then maybe other friendships could really matter too.
Katherine led Damon to waste himself, to sacrifice every bond but the all-encompassing one he so eagerly sought with her. Elena led Damon to do just the opposite. Our of love for her, he built everything he’d been willing to crush for Katherine, including his relationship with his brother.
Though God knows where that’s going to be at now, lol. But that’s another story.
Anyway, the point of that very long-winded segway into Damon/Elena fangirling was to say that if Damon cares for Jeremy, maybe it’s just because of Elena. But only in the sense that all of the caring that he does is because of Elena. I think he loves Jer. Or I think he would love Jer very easily if he felt he was allowed to. So maybe once he’s died for him, thereby redressing the balance for that time he killed him… maybe he’ll feel like he’s allowed to love him. Maybe Jer will let him.
Honestly, I think Jer has always liked Damon. And I know some people were upset that he would question whether Damon cares about him, but honestly I just found it adorable. Basically it was like, ‘You don’t even love me at all, do you???!!!! DO YOU?????? Do you… please?’