Nina Dobrev and Ian Somerhalder
04/24/2012 at 06:00 AM EDT
Ian Somerhalder and Nina Dobrev arrived separately and refused to pose together on the red carpet when the Vampire Diaries actor hosted The Influence Affair, an environmental benefit, at a private home in Bel Air, Calif., on Saturday – but that didn't mean the private twosome stayed apart for long.
"They sat together at dinner, and when Ian noticed Nina was shivering, he offered her his blazer to keep her warm," an onlooker tells PEOPLE of the event, co-sponsored by VeeV. "There was no overt PDA, but there was a certain lovey way about how they looked at each other."
Following a show by graffiti artist Erik Wahl, the pair quietly slipped away for a little one-on-one time during a tour of the mansion where the event was held.
"They were holding hands during the tour," the source says. "They seemed very close and comfortable together."
– Dahvi Shira