How will Cory Monteith's on- and off-screen girlfriend Lea Michele cope with his death?

LOS ANGELES – As family, friends and fans mourn the sudden death of 31-year-old “Glee” star Cory Monteith, none are perhaps more deeply impacted than his on-screen love interest and off-screen girlfriend, Lea Michele.

For Michele, 26, the loss is twofold, as she must first deal with the loss of her boyfriend, and then turn around and act out her loss on “Glee” when producers and writers figure out how to deal with Monteith’s character’s absence. The show is scheduled to begin filming its fifth season in mid-August.

A representative for Michele said in a statement late Tuesday, "Lea is deeply grateful for all the love and support she's received from family, friends, and fans. Since Cory's passing, Lea has been grieving alongside his family and making appropriate arrangements with them. They are supporting each other as they endure this profound loss together. We continue to ask the media to respect the privacy of Lea and Cory's family."

A source close to Michele told FOX411’s Pop Tarts column the two were happy and very much together at the time of Monteith’s death.

“It’s hard to imagine how she’ll cope,” the source said.

We talked to mental health experts about what Michele is going to have to process in the coming days.

“Obviously this is a devastating time for Lea. She and Cory have grown BIG together, they understand the trials and toils of success, and they have held hands through it both as stars on the journey and real-life lovers,” said Sheri Meyers, Psy.D Licensed Marriage & Family Therapist. “The end of a relationship and sudden loss of someone you love causes your brain and body to go through actual withdrawal symptoms.  She may be on an emotional roller coaster for awhile. Giving her the privacy she wants, along with the support she needs and time to heal is tantamount.”

Therapist Dr. Nancy Irwin told FOX411’s Pop Tarts column Michele could at least “take comfort in the fact that she apparently did everything in her power to support the recovery of Cory. It may be quite difficult for her to get back to work, yet the set of ‘Glee’ may be just what she needs to honor Cory’s life and death, to give it meaning.”

Michele has yet to comment, and her rep has asked “that everyone kindly respect Lea’s privacy during this devastating time.”

Rumors first circulated that the co-stars were more than friends in 2011. Michele split with her Broadway beau Theo Stockman, and a few months later she and Monteith was spotted together. On Valentine’s Day in February 2012, the two went public with their romance.

From that point, Monteith and Michele were inseparable, traveling to each other’s home towns as well as Cabo, Mexico, the Coachella Musical Festival in Palm Springs, Calif., and Hawaii. The affectionate duo never shied away from supporting each other at red carpet events or at sporting events. Recently, the couple posted a picture of themselves on social media cheering on the Vancouver Canucks during a game against the San Jose Sharks at Vancouver’s Rogers Arena.

Monteith and Michele embarked on another Mexico vacation in April, just days after he completed a 30-day stint in rehab for substance addiction. The sweethearts made what would be their final public appearance together at the 12th Annual Chrysalis Butterfly Ball in Los Angeles on June 8.

“He seemed great. He was totally normal, happy and fine,” a source connected to the event said. “He was a bit nervous because it was his first red carpet post- rehab, but he was such a huge advocate of Chrysalis, it meant a lot for him to be there. He and Lea seemed so happy. It is such a tragedy.”

Despite his substance abuse issues, Monteith always came across as humble and articulate, and was very well-liked by the press. And while so many couples in Hollywood avoid discussing their significant other in the press, Michele was always open and vocal about her affection for Monteith.

“I don’t even remember a time when he wasn’t my boyfriend. No one knows me better than Cory. No one knows what it’s been like to go through this more than he does,” she told Marie Claire magazine. “Feeling like you have that net underneath you allows you to jump higher and go farther…He makes me feel like I can do anything. For the first time in my life, I feel really, really settled and happy. I feel like the luckiest girl in the world.”