[Warning: This story contains spoilers from Thursday's two-hour Grey's Anatomy season premiere.]

In its first nine seasons, ABC's Grey's Anatomy has always broken ground by featuring stories that have never typically been in the spotlight, including lesbian weddings, PTSD and abortion.

During Thursday's 10th season premiere, the Shonda Rhimes medical drama opened the door to tell a story that hasn't really been featured on the small screen: a lesbian custody battle -- and potentially a lesbian divorce.

Grey's Anatomy's Callie (Sara Ramirez) and Arizona (Jessica Capshaw) began to see their marriage crumble in the season nine finale when the latter cheated on her wife, opening the door to explore both subjects. The story comes as the lesbian, gay, bisexual and transgender community has always pushed for equality when it comes to storytelling, encouraging producers to feature same-sex couples and share the same important moments as their heterosexual counterparts.

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On Thursday, Callie made Arizona's infidelity public knowledge and took things a step further when she moved out of the couple's home and took their young daughter with her.

"Callie decides she needs space and she can't deal with all of these feelings. She's reactive and acting out, and part of the way that she finds solace is to move out of their apartment," Ramirez told The Hollywood Reporter during a recent visit to Grey's Anatomy's Hollywood set. "Initially, she's looking to get some space and to breathe because she's dealing with her own emotions and reactions to what happened. She's dealing with Arizona trying to engage her about it. In the midst of work and the other stresses the last thing she needs is to have somebody over her shoulder wanting to engage about it."

Callie's decision -- while not permanent (as Ramirez notes Callie didn't completely move out of their home) -- leaves Arizona angry and in tears that she will only have custody every other two days until the couple can find a more permanent solution.

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"Callie is trying to juggle how to trust Arizona with Sofia," Ramirez explains. "Obviously, there's custody to think about. You have to figure out how you're going to share your child with her other mother in the midst of all this anger. That's tough. Callie's having a hard time being selfless; she's being selfish and she's trying to be a good mother because ultimately she doesn't trust Arizona anymore."

After Arizona tracks Callie down to Meredith's (Ellen Pompeo) home, the couple engage in a screaming match that becomes so nasty that it leaves poor Derek (Patrick Dempsey) on the front porch with his two young kids.

"It's going to get uncomfortable," Ramirez warns. "It's like in real life how frustrating an uncomfortable situation is when two people don't see eye to eye and a child is involved. Sometimes you can't see the forest through the trees, and both Arizona and Callie are in a really uncomfortable situation and Callie isn't ready to engage about any of it with Arizona."

While Ramirez says divorce "doesn't get brought up," the couple must contend with the trust that is broken -- not just from Arizona's cheating but Callie's broken promise that she wouldn't let anyone amputate her wife's leg after the plane crash.

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"The infidelity is just the surface of what's really going on," Ramirez explains. "There's more to it; it's not clear-cut what the right or wrong answer is in that situation. The way it plays out you can totally understand where each character is coming from. It can be so uncomfortable to see two sides of the story unfold and not see them meet in the middle."

For her part, Capshaw tells THR that this is "not a good time" for the couple, who could potentially seek counseling and/or therapy as they deal with all the issues on their very full plate. "There's going to be a lot of starts and stops, but it's definitely not looking good for them."

"This is a long road and who knows where it's going to end up," Capshaw notes. "In understanding why Arizona did what she did, she might be coming to a place in understanding herself in a way that maybe Callie might not want to be with her -- or Arizona might not want to be with Callie. When something like this happens, it's not like she didn't take out the trash; she slept with someone else. It's as big as it gets and they have to now figure out what that means."

While Arizona showed her ugly side -- freaking out at a nurse who was unwilling to page Callie for a non-medical emergency and screaming at her wife in front of Derek -- Capshaw says she doesn't think either Callie or Arizona will get ugly when it comes to the custody battle for Sofia.

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"They're in pain and there's disappointment and they're feeling deceived, but I don't see them as people who will be ugly," she says. "Arizona needs to get to someplace where she's open to counseling. I don't think Arizona dealt with her pain or grief or anything from the plane crash."

In terms of the couple's long-term outlook, Capshaw is optimistic that the duo can get to a place of understanding.

"I think that there is hope that they will get to a place where they can understand each other a little bit better and then be able to make choices about what is best for each of them," she says. "I think they will find their way to what makes them happy. Whether that's together or apart, I don't know. That's where the story is."

Rhimes, talking to THR in August, said Callie and Arizona's journey this season isn't necessarily about what we've seen or haven't seen before on TV.

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"We let all the other characters on Grey's Anatomy go through everything. It puts Callie and Arizona in a lesbian ghetto the way it does when there's a black character on TV and they always have to be good and can't do anything wrong. It puts them into a lesbian ghetto if they can only be happy and perfectly married," she said. "Let's let them be complex. Let's let them have the same three-dimensional storylines that every other character on television has. Let's let people root for them to get back together or root for them to grow apart. Let's let them have everything that everybody else has; why do they have to be perfect?"

What do you think of Callie and Arizona's current storyline? Hit the comments below with your thoughts. Grey's Anatomy airs on Thursdays at 9 p.m. on ABC.

E-mail: Lesley.Goldberg@THR.com

Twitter: @Snoodit