I would like to point out that Damon spent the entire episode trying to get Enzo back and then was going to chase after him and go off to other places with him to try to get him back

but in season 3 when Elena’s only mission was to get Stefan back, Damon looked her in the eye and told her to give up on him, that he was gone for good. even though he wasn’t and Elena knew that.

Damon put more effort in getting an emotionless friend back than he did for his own brother.