Relationships can be tricky ... especially when it comes to the Kardashians.

On Sunday's episode of Keeping Up With the Kardashians, Kim and Khloe Kardashian awkwardly call out their older sister, Kourtney, for being a little too close to their mother Kris Jenner's boyfriend, Corey Gamble.

"Him and Kourtney, they go out at night together, they hang out during the day, they go on hikes," Kim, 35, tells the cameras. "They are always together. I think I need to talk to Kourtney just to call her out on it."

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Kim was particularly bothered by a photo of Kourtney, 37, and Corey, 35, hiking with two of Kourtney's children with her ex, Scott Disick -- 6-year-old Mason and 3-year-old Penelope.

"That looked like a family photo!" Kim says, calling the two's relationship "weird." "That was so inappropriate. I was, like, uncomfortable. Like, out of this world."

For her part, Khloe wholeheartedly agreed.

"That was the nail in the coffin for me," the 31-year-old reality star expressed about the photo. "I love Corey, I think he's super nice, but I don't ask him to hang out. Kourtney and Corey are, like, conjoined twins."

However, Kim later changed her tune after Kourtney suggested that she get to know their mother's boyfriend of more than a year and a half "better." Corey eventually shared that he was never close to his own family growing up except for his father, which is why he enjoys the Kardashian family dynamic so much.

"I hear about Corey's life and it makes me feel very lucky to have such a big family," Kim said. "[The conversation] made it all come together and makes sense to me why he loves spending time with Kourtney and the kids."

Corey and Kris have been dating since November 2014. Of course, perhaps it shouldn't be too surprising that he's close to the Kardashian sisters, given that he's closer to age to them than Kris, who turned 60 last November.

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Last October, Khloe and her BFF, Malika Haqq, uncomfortably grilled Corey on his intentions with Kris over dinner during an episode of Keeping Up With the Kardashians. However, Corey -- who admitted he'd always been attracted to older women -- handled the sensitive questions about wanting to get married and if he wanted any kids of his own like a total pro.

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