By Emily Strohm
July 15, 2020 at 04:00 PM EDT

As Naya Rivera's family mourns the Glee star’s tragic death, her ex-husband Ryan Dorsey is still reeling from the news.

“Ryan has barely slept,” a source says in the latest issue of PEOPLE. “It’s just a nightmare. Although he wasn’t with Naya, it’s Josey’s mom. Josey needs his mom.”

On Monday, authorities found Rivera's body five days after her disappearance. The actress had gone missing during a boat outing with her and Dorsey's 4-year-old son, Josey, at Lake Piru in Ventura County, California, last week. She was 33.

Despite being found alone on the pontoon boat, authorities said Josey was "in good health," and he was reunited with Dorsey.

“Ryan can’t imagine raising Josey without Naya. It’s the most devastating situation," the source says about Dorsey, who was married to Rivera from 2014 to 2018.

Authorities said Monday that they believe Rivera died saving Josey.

"We know from speaking with her son, that he and Naya swam in the lake together at some point during their journey," Ventura County Sheriff Bill Ayub said at a news conference. "It was during that time that her son described being helped into the boat by Naya, who boosted him onto the deck from behind. He told investigators that he looked back and saw her disappear under the surface of the water."

"The idea perhaps being that the boat started drifting, it was unanchored, and that she mustered enough energy to get her son back onto the boat, but not enough to save herself," Ayub said.

One day before her body was found, Dorsey was spotted at Lake Piru.

Dorsey, 36, ventured into the water with Rivera's family, including her father George, who first arrived at the lake several days prior, as seen in a photo obtained by TMZ.

"Since Naya disappeared, Ryan and Josey have spent every day with Naya's family," the source adds. "They are all supporting each other while also taking care of Josey."

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