Damon has touched a lot of dead bodies before, and he is now utterly, panicking-ly aware that Bonnie Bennett is dead. His intense love of Elena Gilbert has actually killed her. He shakes her again like that might wake her up. He considers trying CPR but he has literally no idea how, but he's going to try anyway because fuck if this is happening right now, fuck if she is dead, no.

She's too dead for vampire blood to bring her back.

"No, no, no, no. Wake up. Elena's gonna lose it if she comes back to you being very dead." He finds the place over her chest where her heart should be and starts wildly doing CPR with chest compressions. "Fuck! You can't die because of me when I didn't even try to kill you so come back or so help me--"

This is not okay. This is not how this works. He kills people when he means to not because he... didn't ,and it's Bonnie, Elena's best friend, and someone he begrudgingly cares about in a way he won't admit (not yet).