Jennifer Aniston & Vince Vaughn’s Steamy Night of Love!

On April 21, Vince was spotted driving up to Jennifer’s house in L.A., and he didn’t leave until the next day, according to Star’s eyewitness.

“Vince didn’t leave until 5 p.m. the next day,� an eyewitness tells Us magazine. But did they hook up ask Us?

If they did, “there is nothing wrong with it,� says an Aniston pal. “She can trust him.�

A Vaughn source agrees: “It’s no big deal if he stayed over. They are friends and can be friends with benefits.�

“It’s difficult for people who have been in a sexual relationship to remain friends,� counters L.A.-based psychologist Ava Cadell. “So the fact that they did remain friends really shows good character and stability.�

Another friend tells Star that these secret get-togethers date back to December, soon after the couple announced their split, but Jennifer Aniston and Vince Vaughn have been careful to keep their recycled love quiet. “Jen’s the resistant one,� confirms a friend.

“She’s let Vince back into her life but only to a point- it’s obvious she’s going out with other guys, as well, which drives him crazy.�

Another source adds that Vince fell into a deep funk after splitting with Jen in December.

“He was in a foul mood while filming Fred Claus in London,� says the source. “He tried to play like he was ok, bu the was hurting. It’s like the light went out of his life. He has been trying to win her back ever since.�

Meanwhile Usmagazine.com is reporting that Jennifer Aniston is closing a deal with Glaceau, the makers of smartwater, to be the face of its next worldwide advertising campaign.

Aniston, who over the years has appeared in ads for everything from Heineken beer to Lynx deodorant, is expected to appear in ads for smartwater, an "electrolyte enhanced" drink with the slogan "water that's the envy of all water."

Says a source close to the deal, "Jen has a clean image and that's smartwater's whole image, so she's perfect for it."