The Glee stars, who play couple Finn and Rachel on the Fox musical drama, have apparently taken their relationship off-screen and begun dating in real life following Michele's split from former boyfriend and Broadway star Theo Stockman in September 2011.
According to Us Weekly, Monteith and Michele recently took a weekend trip to New York City together, as the actress "didn't want to be away from him for just those few days".
A source told the publication: "Cory is definitely having a positive effect on Lea. She's much less miserable these days.
"Even when she was with Theo, she was always depressed being so far away from him and not getting to see him. She likes having someone with her that's actually there. Long-distance is not her thing."
Michele said in October 2011 that she was happy to be single after ending her relationship with Stockman.
Watch Lea Michele's Glee performance of 'Here's To Us' below: