Somerhalder has now told Zap2It that Damon will not hold much hope that Stefan will return.
"Damon knows this cycle with his brother," he said. "He's seen it before, totally. He says to Elena, 'Stefan's not coming back. Not in your lifetime'. I mean, she's young, but human beings only live maybe 80 years. For Stefan and Damon, that's nothing. Unless Klaus rips their hearts out, they're going to live for another thousand years."
Somerhalder added: "I don't think that Damon's focus is really to save Stefan, because he understands that if Stefan doesn't want to be found, he's not going to be. And in some weird way Damon respects that. He's been there too, not very long ago."
Somerhalder also revealed that Damon will be "pissed off" with Stefan when he finally returns.
"For two seasons he tried to get Stefan to do exactly what he's doing now, to drink blood with Damon," he said. "And now he's running off doing exactly that thing, but with some asshole that Damon can't stand. A guy that tried to kill Damon and everyone they care about."
Somerhalder explained that Elena is a "girl that [Damon] loves, but that he can't have, because it's his brother's girl", and continued: "When he finally sees Stefan, it's like, 'I tried for two seasons to get you to do this and now you're off running around with this idiot'.
"That's all Damon wanted in season one, was his brother to run around with him and munch on sorority girls and bring down the house wherever they went, and Stefan said no. Now he's left Damon here all by himself, to fend for himself, and protect this girl who is 150 years his junior. He's not happy about it."
The Vampire Diaries returns for its third season on September 15 on The CW.