The Alpha Dog star, 24, has been dating Domont, 20, since 2008.
According to U.S. magazine Star, the couple ended its relationship earlier this year (10), amid reports Hirsch wasn't ready to take their relationship to the next level.
A source explains, "Emile really cares for Brianna, but he was starting to feel too settled, like an old married man."
A spokesperson for Hirsch had not responded to requests for comment as WENN went to press.
The actor joined other celebrities including Jessica Biel and rapper Lupe Fiasco for the trek up the African peak in January (10).
But Hirsch's trip was almost cut short after an ingrown hair in his groin became infected, hindering his efforts to scale the mountain.
He tells JustJared.com, "I had an ingrown hair in my groin, so I couldn't walk! I don't like to talk about it because it got infected, there was pus and it was nasty. There was a 90 per cent chance they would have had to medevac (medical evacuation) me out of there but thankfully my condition improved and I finished the climb."
Jesse James Hollywood was sentenced on Friday (05Feb10), 10 years after he led a gang murder of Nicholas Markowitz in California.
Prosecutors maintained Hollywood was the ringleader of a plot to kill Markowitz to send a message to the teenager's brother after he failed to pay off a drug debt.
The killer was captured in Brazil five years after he disappeared from California.
His arrest came just before director Nick Cassavetes' Alpha Dog, which starred Emile Hirsch and Justin Timberlake, was released.
The Illusionist actress hiked to the top of the 19,340-foot-high (5,895-metre) Tanzanian peak with a team of celebrities, including actor Emile Hirsch and rapper Lupe Fiasco, for a charity campaign last month (Jan10).
But she won't be revisiting Kilimanjaro in the future - because finishing the mission was too physically demanding.
She says, "I'm never going to do that again... It was incredible. It was such a challenge for me. It was probably one of the hardest things I've ever done... sometimes it was kind of miserable.
"Altitude sickness is like a general uncomfortable, uneasy feeling. You just can't think straight. (But) hiking for seven hours a day and sleeping in tents and being out in the wilderness was a real experience everyone should try."
Rich, who worked in casting for Rodgers and Hammerstein and MGM and famed Broadway producer/director Harold Prince, died of natural causes on 28 December (09).
She also ran her own agency for three decades, Shirley Rich Casting.
Rich placed Hirsch in 1973 film Serpico and cast Penn and Cruise as military cadets in 1981 film Taps. She also cast actors James Spader, Edward Norton, Rod Steiger and Sada Thompson early in their careers.
On Broadway, she cast shows including South Pacific, Fiddler on the Roof, Cabaret, The Kind and I, The Sign in Sidney Brustein’s Window and Sly Fox, among others. On film, she scouted talent for Saturday Night Fever, Three Days of the Condor, Kramer vs. Kramer and The Ballad of the Sad Cafe.
Rich is survived by her husband, Lewis M. Krohn, a son, Steven, and a daughter, Lisa.
Jessica Biel, Emile Hirsch, Lupe Fiasco and Santigold star Santi White are among the group hoping to raise cash and awareness about the world's chronic water shortage by signing up for the charity climb to the 19,340-foot (5,895-metre) peak.
The Summit on the Summit posse set off on Thursday (07Jan10) and have been using the latest social networking technology to update fans and followers along the way.
In a recent 'tweet', climber Alexandra Costeau - the granddaughter of adventurer Jacques Costeau - writes, "2morrow we summit at dawn!"
And singer Kenna - the celebrity behind the big climb idea - adds, "Morning of. Actually slept. Can't believe it. This is it. This is the last day. We feel the Love."
The two movie stars have been joined by actress Isabel Lucas and pop stars Santi White, Lupe Fiasco and Kenna on the trek to the top of the 19,340-foot peak.
The star-studded group began the climb on Thursday (07Jan10) and are using the latest social networking technology to update fans and followers along the way.
They'll be posting posting clips, photos and 'tweets' on the Summit on the Summit website.
The Into the Wild star will don his climbing gear on Thursday (07Jan10) to scale the 19,341-foot (5,895-metre) African peak to fundraise and highlight the need for clean drinking water in less economically developed countries.
Hirsch is looking forward to tackling the climb, branding it "an epic adventure with an educational process on the global water crisis", and he's determined to reach the mountain's highest point.
He adds, "Put this on the books: I'm making it to the top."
Transformers: Revenge of the Fallen actress Isabel Lucas and rapper Lupe Fiasco are also taking part in the Summit on the Summit expedition.
The busty blonde claims an explicit video set to be released by Vivid Entertainment has been acquired illegally and the company's bosses have no legal right to distribute the racy footage.
She tells TMZ.com, "Yes, I did make a sex tape with my boyfriend earlier this year. In fact, I've made several sex tapes, but I certainly didn't sign off on this and Vivid has no right to put it out. I am trying to get a hold of my attorney now."
Sand wants to block the adult footage from being released to the public, but Vivid boss Steven Hirsch is confident his company has done nothing wrong.
He says, "We were approached by a third party, who brought us footage of Shauna having sex with her current boyfriend and we were immediately interested in acquiring it... We're comfortable with out legal position in releasing this footage."