Let's be honest, when you're in a relationship you get to know a lot about that person, we're talking stuff you'd never share with any other soul. But is there a point where things can go too far?
Well, former flames Delta Goodrem and Brian McFadden certainly tested the limits.
A former pal of the pair, Kyle Sanders, opened up about a particular game the couple used to play when they were together, and the thought of it isn't pleasant.
Speaking on KIIS FM, Kyle said the pair would "spit in each other's mouth".
Co-host Jackie O then voiced the question on everyone's mind: "Why?"
"Fun, they said fun," Kyle replied. "But I always thought, 'Wow! That's weird."
"Delta would sit with her mouth open and Brian would spit into her mouth and Delta would spit back into his mouth."
We'll just allow the shudders to pass for a moment here.
McFadden and Goodrem started dating in 2004 and were engaged in 2007. In 2011, the pair split.
In 2012, Goodrem opened up about the break-up, telling Vogue she was "really unhappy" in the relationship and didn't know how to get out.
Since Brian, Delta has been romantically linked to Nick Jonas, who is now engaged to actress Priyanka Chopra. She also dated Aussie musician Matthew Copley.
Earlier this year, Woman's Day revealed Delta was feeling heart broken over Nick.
"Delta was left heartbroken [following news of Nick's whirlwind romance with Priyanka]. She feels she can't compete with a hottie from Hollywood, whose best friends are royals," a source said.
"She began to miss Nick soon after she dumped Matthew. Delta realised Matthew wasn't right for her, which is why being back with Nick felt so right."
Meanwhile, rumours are rife that Delta has since got back together with Matthew when the pair were spotted sharing a lingering hug, according to New Idea.
In April, the singer said she would not discuss her relationships unless she absolutely had to.
"All I've kept saying is, 'I'm single and I'll let you know when I'm in a serious relationship.' And I will," she told In Style.
WATCH: Ed Sheeran admits 13 year old crush on Delta Goodrem:
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The judge on The Voice also scored the lead role in the television biopoic Olivia Newton-John: Hopelessly Devoted To You, which aired this year.
The 33-year-old recently broke down on Sunday Night when she talked about portraying her beloved friend Olivia.
"When I look at her... I find it so hard because it's quite personal actually," admitted Delta while fighting back the tears.
Delta opened up about how her own diagnosis with Hodgkin's lymphoma when she was just a teenager made the scenes dealing with Newton John's cancer battle hard to tackle.
"I had to reopen old wounds that I had already stitched up," she told the Herald Sun.