Lambert, 31, confirmed his split from Koskinen in an interview with South Florida Gay News on April 5, reported Ace Showbiz.
"It's been kind of on its way out in the last couple of months.
"Sauli and I remain really good friends, and I know it's a cliche thing to say. But it's totally true. I just gave him a coffee and bagel earlier today. He's a great person and we've had an amazing couple of years together. Things have just run their course," he said.
"I've been getting really busy and traveling a lot and and he's been getting really busy because he has a show he's filming for Finnish television. So we just decided to part ways," the 31-year-old singer said.