Nicole Simpson Brown's ex-boyfriend is relieved now that O.J. Simpson has died -- saying the news has left him with a smile on his face ... this, 30 years after her tragic murder.

Keith Zlomsowitch -- who dated Nicole in the early '90s, after she'd divorced O.J. -- dropped by on "TMZ Live" Thursday to talk about the news ... telling us he's glad O.J.'s now gone from this Earth, ending a long and painful saga for him.

Keith says with O.J. dead ... he won't be able to inflict any more pain or emotional stress on anyone else -- it goes without saying .. Keith is in the camp of folks who believe he did it.

However, KZ points out while he's glad O.J.'s passed on, that in and of itself doesn't bring back Nicole or Ron Goldman, who were brutally slain in '94. He says his heart breaks over the fact he missed out on 3 decades' worth of friendship and time with Nicole.

Keith also recounts all the threats and stalking he says he and Nicole were subjected to by O.J. while they were dating ... memories which only reinforce his comfort over his death. It was well-chronicled at the time ... Nicole had alleged domestic violence against O.J., and even once called 911 to report him.

Keith expressed deep sadness about the ordeal Nicole went through because of their relationship, and in the aftermath of O.J.'s death ... he still only thinks of Nicole.

Simpson became the LAPD's prime suspect in the murders of Nicole and her friend Ron. The infamous low-speed car chase ensued, ending with his arrest at his Brentwood home.