Michael Houston sat down with his mother Cissy and spilled his guts to Her Royal O-ness on "Oprah's Next Chapter" ... admitting he was the first person who did drugs with Whitney.
Michael says he feels extremely guilty for Whitney's death -- but says he didn't realize how deadly drugs could be when he first brought them to Whitney's doorstep ... explaining, "You gotta understand at the time ... the 80s ... it was acceptable."
Houston adds, "It's painful ... I feel responsible for what I let go so far."
Whitney died in Beverly Hills last February after a drug binge that included cocaine, Xanax and marijuana.
"Acceptable"? Really, Mike?
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