Justin Bieber & Selena Gomez Back Together in a Big Way (VIDEO)

6/17/2014 7:42 AM PDT

Selena Gomez is back on the Bieber train ... clutching and grabbing onto him on Monday night after a day of Malibu fun.

Our video tells the story ... Justin and Selena partied together at Bootsy Bellows --at a birthday celebration for a friend  -- and it appears she never left his side.

Earlier in the day ... Selena was riding bitch with Justin on his Can-Am Spyder 3-wheeler as they cruised along the beach with a group of friends.

You may recall ... Bieber Instagrammed last week, "Our love is unconditional."

Selena was right about needing rehab ... she's addicted to Bieber.