Lamar Odom WAS With Khloe Kardashian -- But They're NOT Back Together

We've just confirmed ... Lamar Odom WAS with Khloe Kardashian last night at Kanye West's concert ... but sources familiar with the situation tell TMZ ... she is NOT reconciling with him.

We're told the reason Lamar was invited ... he's been clean and sober for several weeks and the Kardashians are "supporting his recovery and wanted him to have a good time."

Lamar showed up by himself, but joined Khloe inside Staples for the concert. We've also confirmed Bruce Jenner was also there. Kris Jenner was there as well, and she hung out with Bruce -- but again, they're not back together either.

Bruce brought his sons, Brody and Brandon.