New legal fallout from 'Scandoval' -- Ariana Madix is suing Tom Sandoval over the Los Angeles house they co-own, and still live in together.

The "Vanderpump Rules" star filed suit against her ex-bf in L.A. Superior Court ... and the docs make it clear they are at loggerheads over how to split up the house.

According to the docs, obtained by TMZ, Ariana says she wants a "partition by sale" ... which means she wants a judge to order them to sell the house, and divide the proceeds.

What she doesn't want is a "division in kind." That would allow each of them to retain their ownership interest in the property ... and one of them could, theoretically, sell to a third party.

Translation: She just wants to sell the place, and have them both move on with their lives.

Back in better times, Tom and Ariana bought the San Fernando Valley home in 2019 for about $2 million.

Despite their relationship blowing up very publicly last year when she found out Tom was having an affair with Rachel Leviss ... they've both continued to live in the home together.

That's about to end ... if Ariana gets her way.