Drew Barrymore and Justin Long
Jon Kopaloff/FilmMagic; Fitzroy Barrett/Landov
is wrapping up her summer of love with the Apple computer commercials' "Mac Guy," Justin Long.
The He's Just Not that Into You
costars seemed really into one another over Labor Day in Vegas, where the two were "all over each other, making out the entire time," a witness at Jet Nightclub tells PEOPLE.
First spotted together at Chateau Marmont on Aug. 28, Barrymore, 32, and Long, 29, brought their holiday weekend to a close back in Los Angeles at a trendy sushi restaurant with friends.
According to a Barrymore pal, "the relationship is very new."
So new, in fact, the actress dallied
star Zach Braff in June and rekindled old flame Spike Jonze in August.
At the end of August, a pal of the actress told PEOPLE, "Drew is crazy about [Jonze]. She's definitely feeling long-term about it. They're really great together."
Reps for both Barrymore and Long had no comment.
Reporting by JEN GARCIA, MARK GRAY and MARY MARGARET