According to his mom, Suzanne, who sat down with the rest of Matthew's family for an interview with "TODAY" for the first anniversary of his death, her son was "so desperate for a solution" to his ongoing addiction problems ... as he felt "it was time" for him to have a wife and kids.

Suzanne suggested these personal goals led Matthew to seek out mental health treatment -- including ketamine infusion therapy -- which MP's mom said had a "frightening aspect" to his medication.

As Matthew's family put it ... he did take his sobriety journey seriously, as he'd drop everything to help someone else in need.

One of Matthew's sisters recalled that he used to say he was "really great at rehab," but "not so great at the time that came after" ... which is not uncommon for people coping with addiction issues.

While his loved ones are able to celebrate his effort now, stepdad Keith Morrison admitted he sometimes would get "mad at him" ... as watching Matthew's addiction struggles unfold was "heartbreaking."

Matthew was found unresponsive in the hot tub of his Los Angeles home on Oct. 28, 2023 ... he was later pronounced dead. It wasn't until December when the Los Angeles County Medical Examiner's Office ruled the actor died from the acute effects of ketamine.

Though Matthew had been receiving the ketamine infusion therapy, he hadn't received treatment in the week and a half leading up to his death ... which prompted an investigation into his passing. Five people have since been arrested in connection with his death.

Matthew's best friends Brian and Chris Murray, who spent his last Christmas with him, insisted the A-lister was on the right path ... writing, reading scripts, and expressing dreams of directing.

His best-selling memoir, "Friends, Lovers, and the Big Terrible Thing," had even put "a massive spark in his step."