Et tu, roomie?

State Sen. Jessica Ramos of Queens caused a stir Thursday by endorsing City Councilwoman Carlina Rivera over Assemblywoman Yuh-Line Niou — Ramos’ onetime roommate — in the hard-fought Democratic primary to represent the 10th Congressional District.

“Carlina shows up for New York’s working families every day, listening to our needs and fighting for our causes, and has worked hard to earn the support of organized labor, with the greatest number of union endorsements in the race,” Ramos said in a statement. “I am proud to endorse mi amiga Carlina, and I know she will make an incredible Member of Congress.”

It’s a far cry from 2019, when fellow lefties Niou, Rivera and state Sen. Alessandra Biaggi shared a $1,200-per-month, seven-bedroom house in Albany and were the subjects of a glowing profile by the New York Times.

The three millennials found common cause criticizing the established ways of Albany – with an aide to then-Gov. Andrew Cuomo infamously calling them ‘f–ing idiots” after they slammed him for holding a fundraising event amid delicate state budget negotiations.

But a rift between Ramos – who backed Bernie Sanders for president in 2020 – and Niou and Biaggi – who supported Elizabeth Warren – ended the trio’s halcyon days and state Sen. Julia Salazar replaced Ramos in the Albany house.

“Ramos, Biaggi and Niou started out as a BFF trio in their early Albany days, and over the course of a couple years, tension grew between Ramos and Niou/Biaggi,” a source familiar with the situation said of Ramos’ support for Rivera. “Part political, part personal. So not surprising to see this.”

One New York Democrat was more blunt, saying that Ramos “knows firsthand that Yuh-Line is crazy,” referring to Niou’s history of political stunts and scathing speeches blasting establishment Dems.

Ramos declined to comment about her endorsement when reached by The Post Thursday. Niou did not respond to a request for comment.

Rivera and Niou are battling to represent the newly-drawn district that straddles lower Manhattan and brownstone Brooklyn, and Ramos’ endorsement is a sign that the councilwoman is consolidating support among Latinos — Reps. Nydia Velasquez and Adriano Espaillat have also backed her in recent days — while wooing progressives away from Niou, who has backing from the left-wing Working Families Party.

“By endorsing Carlina, [Ramos] was able to endorse a progressive candidate who is a Latina womxn,” political consultant Camille Rivera told The Post in a text message. “We also can’t ignore that the district has a sizable Latino population.”

“She is a genuine champion of working families who never backs down, and I’m honored that she has endorsed me to carry that spirit into Congress,” Rivera said in a statement thanking Ramos for her backing.

Recent polling suggests former House impeachment lawyer Daniel Goldman has a slight edge in the race following his endorsement by the New York Times editorial board and the final debate of the campaign Wednesday night.

Primary voting ends Aug. 23, with Republicans standing no chance of winning the deep-blue waterfront district.