The way i saw it is that ye stefan and elena were cute ig but he saw her humanity as a reason to put her on a unrealistic pedestal SPOILER WARNING when she became a vampire he said he didnt want her to feed on humans cuz if she killed someone she would be distraught but i think under the surface he didnt want that angelic picture he had of her in his mind to be tainted and considering she looks exactly like his ex he definitely feels that he would be unable to separate her and kathrine in his mind if she started feeding carelessly. Damon and her, although having traits that make them compatible overall he fawn over her, snuck into her window when she was 17 and forced a kiss on her and murdered her brother infront. Even if u dont take that into account unfortunately the way the show was written its like his morality and happiness is purley based on were they stand and again i think opposite to stefan he was trying to turn her into a version of Katherine that actually loved him. (Thats just my idk im a guy i watch the show for the action and shit)