"The Real Housewives of Beverly Hills" star draws her line in the sand in a preview for an upcoming episode of the reality show ... though, interestingly, she makes the statement to castmate Dorit Kemsley -- not Mauricio -- saying, "If there's no effort, we're not going to end up together."

She's clearly discussing the elephant in the room this season ... the fact she and Mauricio have been estranged for several months now, but still living under the same roof with their children.

In the teaser clip, Mauricio leaves Kyle to go show some homes for The Agency -- and then she meets with Dorit to give her the lowdown on her marital struggles.

The issue, according to Kyle, is Mauricio's major focus on his booming real estate company, which touts itself as a billion-dollar brokerage firm.

Kyle grumbles to Dorit ... "He has to say yes to more things because the Agency is expanding so much. So I'm like, if we're having an issue why can't you give that energy that you give to the company?"

Obviously, Kyle is not mincing words. She wants a lot more from Mauricio or their relationship could be kaput.

What she doesn't discuss -- at least, in the clip -- is the fact they've both been seen out with other people, boosting rumors about divorce. Kyle's been hanging with Morgan Wade, who she insists is just a friend, and Mauricio partied hard in Aspen with other women.

Kyle and Mauricio officially separated after 27 years of marriage in July 2023. They have 3 daughters: Alexia, 27, Sophia, 23, and Portia, 15.