Myla Sinanaj -- Kris Humphries' Mercedes is MINE Now

Kris Humphries and his on-again girlfriend Myla Sinanaj are so chummy ... the NBA star actually gave Myla his ridiculously expensive Mercedes-Benz -- at least for now.

Myla arrived home to her house today in Rutherford, NJ driving Kris' white Mercedes -- and we KNOW it's his Mercedes because he's been driving the same car forever ... long before Myla even entered the picture.

We asked Myla what she was doing in the whip, and she insisted, "It's my car. It's not his car."

Which means she's either bending the truth, or Kris actually gave her the ride. In either case, it's obvious things are heating up between the two.

Nevertheless, Myla says, "We're just friends, hanging out."