US Weekly reports:

On July 7, Michael Jackson's family ­gathered to celebrate him at his much-watched memorial service.

Noticeably absent?

Janet ­Jackson's longtime music-exec boyfriend, Jermaine Dupri. (A pal says Dupri skipped the memorial because he "doesn't attend funerals.")

And for good reason. "His friends are telling people it's over," a source tells the new issue of Us Weekly, on stands now.

Echoes another: "They have been moving in different directions for a while."

So what drove Jackson, 43, and Dupri, 36, apart after nearly seven years?

"You shouldn't mix business with pleasure," a mutual pal explains. (Dupri produced several tracks on her last two CDs.) "Janet felt their lives were too crossed and they should have kept things sepa­rate."

Plus, the polar opposites were never too compatible.

"Jermaine likes to be out there, mingling with everybody, and ­Janet's more shy." (And secretive: She kept her nine-year marriage to Rene Elizondo hidden until their 2000 ­divorce.)

Meanwhile, Jackson is still deeply mourning the death of her big brother.

"She's devastated," an insider says. "She's busy caring for Michael's kids. Janet's the family's backbone."