Ashlee Simpson has left her boyfriend Braxton Olita to chase Fall Out Boy rocker Pete Wentz reports NW Magazine.

Last week, Ashlee was accompanied by Fall Out Boy bassist Pete Wentz to MisShapes. , Ashlee straddled Pete, according to a fellow reveler, reports Radar.

Partying with an actual rock star apparently proved too much for young Ashlee, who had to excuse herself to vomit. Management kindly blocked off the bathroom to let her retch in peace .

Just days before, while at the Roxy with Jess, Ashlee met up with Pete, inviting him to join the girls when they left for the G Spa & Lounge. Once there, the couple sat in a corner, where onlookers say they cuddled up and whispered to each other for the rest of the night.

Sources say Ashlee may have dumped Braxton - a guitarist in her backing band - as revenge for his public criticism of her radical makeover, which includes plastic surgery and drastic weight loss. “Braxton likes Ashlee the way she used to look,” reveals a pal.

Insiders claim the couple broke up about a week ago. “They have decided to take a break,” a source confirms.

It leaves Ashlee free to date Pete, 27, who has reportedly ditched his girlfriend, former Buffy the Vampire Slayer star Michelle Trachtenberg.

But while Braxton, 20, is devastated, sources say her interfering dad and manager Joe is happy about the split. Insiders say he urged Ashlee to dump the musician and start dating an A-lister in a bid to raise her profile.

He’s even picked out a guy, reportedly trying to set up his 21-year-old daughter with Matthew McConaughey, 36. “Joe went so far as to call Matthew’s people to suggest a date, but they turned him down,” a source reveals.