Hargitay, 57, met Hermann, 53, when the actor first appeared on SVU in 2002, and while he's since guest-starred more than 30 times, he's been MIA for the past four years.
"Mariska is dying to have him back on the set, but he's busy with his own TV career," says the source, who points out that Hermann is a cast member on Younger and has a recurring role on the hit police drama Blue Bloods.
"Mariska never expected SVU would have such a long run, and she's considered leaving the show so she can spend more time with her family [the couple share kids August, 14, Amaya, 10, and Andrew, 9]," the source shares. "Unless they can find a way to work out their schedules, Mariska worries that she and Peter will be ships just passing in the night.
"Mariska loves working with Peter," says the source of the couple and occasional costars.
The United 93 actor previously said that the recipe for everlasting marital success was that they always manage to "find their way back to each other."
“It’s this fantastically, wonderfully ridiculous way that we can swing back and forth any number of times in any given day. But fundamentally we know we have the same destination," Hermann said of his relationship. "We know where we’re headed, and it’s good. And we know we’ll get there together."
After meeting on the set of Law & Order, the two tied the knot in 2004. "I was tingly and jittery and different and excited and nervous and alive," Hargitay later said about marrying her co-star.