Ryan Dorsey, the former partner of Naya Rivera, has shared a heartbreaking revelation about the day the Glee actress tragically passed away at the age of 33 on July 8, 2020.

In an exclusive interview with PEOPLE, Dorsey, 41, spoke about their son Josey, now 9, who still carries guilt over not being able to save his mother. He recalled that Josey, who was just 4 at the time, tried to throw a rope to Rivera while they were swimming in Lake Piru, California, but was too scared because of a spider on it. “He keeps saying he was looking for a life raft, but the rope had a big spider on it, and he was too frightened to use it,” Dorsey shared. He constantly reassures his son, telling him, “Buddy, that rope wouldn’t have been long enough.”

Josey also remembers that the weather was windy that day, and though he was hesitant to get into the water, his mother encouraged him, saying, “Don’t be silly!” After they swam for a while, Rivera realized their rental boat—lacking an anchor or flotation devices, as noted in the wrongful death lawsuit Dorsey later filed against Ventura County—was drifting away. She instructed Josey to swim back, and he managed to grab onto the boat and pull himself aboard. According to reports, Rivera drowned after using her last bit of strength to ensure her son’s safety.

“The last thing she said was his name before she went under, and he never saw her again,” Dorsey revealed. “It’s devastating to know he had to witness her final moments.”

Dorsey learned that Rivera was missing through a call from her mother’s husband while he was grocery shopping in Big Bear Lake, California. Overcome with panic, he collapsed onto a stack of drinks. “I feared the worst,” he admitted.

Immediately, he got into his car and raced 145 miles to Lake Piru. “I was driving over 100 miles per hour with my hazard lights on, chain-smoking cigarettes—even though I don’t really smoke—and just crying,” he recalled. “All I wanted was to get to Josey.”

Josey was found asleep and alone on the drifting pontoon boat that Rivera had rented just hours earlier. Reflecting on that terrifying moment, Dorsey admitted, “If we had lost both Naya and Josey that day, I don’t know how I would have gone on.”