Nick Lachey recently confirmed that he and Vanessa Minnillo are back on. That news dashed Jessica Simpson’s hopes that her missing dog, Daisy, would bring her and her ex-husband back together again, Fox411 has learned.

Nick said about his reconciliation with Vanessa, “We don’t know what the future holds. I’ve given up trying to figure that out. But everything’s going good again.”

SLIDESHOW: Click for pics of Jessica in good times and bad.

A source says upon hearing this, Jessica suffered a major meltdown.

“Jessica is at an all-time low since her recent breakup with Tony Romo and the disappearance of her most cherished companion, Daisy,” the source tells Fox411.

Daisy was snatched by a coyote in September.

“She somehow got it in her head that Nick and her would reunite over losing Daisy, since [Daisy] is really Nick’s dog too,” the pal explains.

Nick gave Daisy to Jessica when they were still married.

But Nick reuniting with Vanessa threw a wrench in her wishes. Jessica found out about their reunion earlier this month in Las Vegas, says the source.

“She was supposed to have a fun Vegas weekend for her sister Ashlee’s birthday party at Wet Republic in the MGM Grand,” the insider tells Fox411. “But the only thing that ended up being wet was Jess’s pillow as soon as she found out Nick and Vanessa were staying at the Venetian right next door for Lavo’s anniversary party.”

“She was not expecting them to get back together, and she took it pretty hard,” the source continues. “Jess can’t handle it. She thought there was maybe a chance for her and Nick in light of their breakups. Jessica thought the timing was just right.”

Wrong.