Lamar Odom/Khloe Kardashian Showdown Over Drugs

Khloe Kardashian had a nuclear confrontation with Lamar Odom that could be the last straw in their marriage ... TMZ has learned.

As TMZ first reported ... Lamar went to their Tarzana house Tuesday ... to pick up some clothes and speak with Khloe. Now we know what was said ... and what she found.

Sources connected with the couple tell TMZ ... Lamar told her he had been sober for 3 days and planned to stay sober on his own ... without going to rehab. We're told Khloe recoiled in anger, telling Lamar he was in denial and needed rehab. She also said she wanted nothing to do with him until he entered an inpatient program.

Our sources say at some point during the meeting, Khloe found a pipe with a stash that looked like crack in a baggie. It's not clear if she found it on his person or the clothes he was picking up from the house.

Sources close to Lamar tell us Khloe went ballistic, calling Lamar a "liar" and telling him, "I'm done with you." Khloe then threw him out of the house.

Our sources say Lamar seemed "out of it" during the meeting and even accused Khloe of stealing his stash.

As for the marriage ... we're told Khloe has "not done anything legal yet," but, as she put it, finding the stash "was the last straw."