Lamar Odom -- Group Therapy at Apartment Building ... with Fans

Lamar Odom is getting a ton of support from fans in downtown L.A. ... where he kept up his strange nocturnal movements Monday night.

We spotted Lamar in his black track suit just after 10 PM in the the lobby of the apartment building where he's now living -- and he was posing for photos with several fans.

Lamar posed for photos with at least 3 fans -- including a middle-aged woman and her family -- before making an exit through the building's parking garage.

Lamar's been seen multiple times in the last few days wandering near the building late at night -- and sure isn't, outwardly anyway, acting like a guy in the grips of a serious crack addiction.

Not to mention being right on the verge of destroying his NBA career, and his marriage to Khloe Kardashian.

Smile and the whole world smiles with you?