Jason Wahler -- Engaged!

Someone's movin' on! Fresh from rehab and a jail stint, former "Laguna Beach" cast member Jason Wahler is making another positive change -- he's getting married!

Wahler's rep confirms to TMZ that Jason proposed last weekend to his USC tennis star girlfriend, Katja Decker-Sadowski. We're told he picked out the four-carat (holla!) emerald cut diamond ring at XVI Karat in Beverly Hills. Take that Spencer and Heidi!

The two, who have been dating for roughly six months (an eternity in MTV reality show years!), recently started shackin' in Los Angeles. They have not set a date.