Things are heating up between 15-year-old Disney starlet Miley Cyrus and her 20-year-old model BF Justin Gaston.

The lovers put on a sickening display of kissing and smooching after Justin’s runway appearance in Christian Audigier’s Spring 2009 as part of Los Angeles Fashion Week on Wednesday, spywitnesses tell The New York Post.

They were “were all over each other backstage.” The heat extended to the runway where, every time Gaston walked, he would blow a kiss and wink at his teenage girlfriend, who in turn, “licked her lips seductively as he passed her.”

Apparently, Miley and Justin are already hosting private slumber parties for two.

The source also overheard a conversation in which Miley told a friend that “she was probably staying at Justin’s tonight and that they were going to skip the after-party and have a party of their own.”

“It’s so funny. Everyone in LA knows that if you want Miley to show up at your event, all you have to do is hire her boyfriend as a model.”