Bulldog to Justin Bieber -- PLEASE PLEASE PLEASE Don't Adopt Me!

Justin Bieber just adopted another pet he will almost certainly abandon ... TMZ has learned.

Justin was at a pet store in Stratford, Canada Thursday ... just to window shop. But then -- sadly -- he fell in love with a 7-week-old American Bulldog named Petey. Justin bought the dog for $600. He also bought dog food (we're guessing the small bag), toys and a collar.

So why you ask are we so cynical? Maybe because Justin once owned a hamster, which he gave away to a random fan -- the critter subsequently bit the dust. He also abandoned a pet monkey in Germany.

It's like Justin is creating his own Neverland -- for pet orphans.