While Matthew Perry's death absolutely floored his fans and close friends, his ex-girlfriend Maeve Quinlan is not in that group, as she says they'd all been losing him to addiction ... little by little for years.

"The Bold and the Beautiful" actress dated the "Friends" star from 2002 until 2003 ... telling Soap Opera Digest he was 100% sober the entire time they were together, which she called the greatest gift for her, and some respite for Matthew from his personal demons.

Maeve said they were inseparable during their year together, and he appreciated being with her because she wasn't using drugs.

For a quick recap, Matthew says he got addicted to Vicodin in 1997 after a jet-ski accident, and sought help in rehab the same year. He headed back to rehab -- for pain meds, amphetamines and alcohol -- the year before meeting Maeve.

His battles started up again after they split, and even though they stayed good pals, Maeve admits she wasn't aware of how much Matthew was struggling because he was always making others laugh.

However, they grew further apart in the last few years ... and Maeve says she has a lot of regret over not reaching out to him after the release of his 2022 memoir, "Friends, Lovers and the Big Terrible Thing."

Given the challenges Matthew faced in life, his October 2023 death didn't come as a surprise to Maeve, but she was still devastated.