Cory Monteith checks into rehab, GF Lea Michele stands by his side

Cory Monteith is seeking help to deal with substance addiction -- and his girlfriend Lea Michele is standing by his side.

The 30-year-old "Glee" actor has "voluntarily admitted himself into a treatment facility for substance addiction," a rep for the actor confirmed to amNewYork on April 1.

"He graciously asks for your respect and privacy as he takes the necessary steps towards recovery," the rep added.

Monteith, who plays straight-laced Finn Hudson on the hit FOX show, has been open about his past struggles with drug abuse; in 2011, he told Parade magazine that by age 16 he had used "anything and everything, as much as possible. I had a serious problem." And at 19, he entered rehab for the first time.

Michele, Monteith's "Glee" co-star and his girlfriend of about a year, is supporting him through his treatment.

"I love and support Cory and will stand by him through this," she told amNewYork in a statement. "I am grateful and proud he made this decision."