Lea Michele has ''really calmed'' Cory Monteith.

The 'Glee' actress, 26, has been a great influence on her 30-year-old co-star and boyfriend, who checked into rehab last week under her advice, and friends have no doubt that she will continue to support him.

A source close to the couple told People.com: ''Lea is an excellent influence on him. She's good for him. She's really calmed him.''

Another source revealed that the duo, who went public with their romance one year ago, are stronger than ever despite Cory's issues.

The insider said: ''They seem to compliment each other's personalities very well. They are always very affectionate and sweet to each other. Cory acts very protective of Lea.''

Despite being a ''low key'' pair when they socialised, other insiders revealed they were occasionally spotted drinking together, saying: ''The two of them drank together, but drank in a way that seemed to be responsible. They both seemed in control and not messy.''

But a friend close to Cory credited Lea for helping him with his ''substance addictions'' before they got out of hand by encouraging him to seek treatment.

He added: ''She would have been very supportive and encouraging for him to seek treatment. It seems like she is a very steady hand.''

Cory - who has been clean since going to rehab at the age of 19 - was reportedly led astray by his Hollywood friends and started drinking and taking drugs at parties at his Hollywood Hills home.

The source previously explained: ''He drinks hard and then he can't say no to other things. The house party scene in Los Angeles is dangerous for him. He thought he could dive in and then drop it but he got hooked on stuff again.

''Rehab can work for him because he's committed. He feels blessed with his life. He realised he needed outside help and he really wants to get back on track.''