Brody Jenner is living the single life again ... we've learned he and Kaitlynn Carter are calling it quits a year after they got married -- or so we thought.

Sources close to the former couple tell TMZ ... Brody and Kaitlynn are done, and she's already moved out of the house they shared together.

We're told Kaitlynn wanted 2 things from Brody -- a baby and a legal marriage -- but Brody ultimately decided he didn't want to do either, so they broke up. She wanted a legal marriage because turns out they never made it official after holding a ceremony last summer in Indonesia.

You'll recall ... Brody and Kaitlynn had a big blowout celebration on the island of Nihi Sumba in June 2018, complete with fireworks -- in the sky and among the guests. Remember, Brody's dad, Caitlyn Jenner, had skipped the nuptials to attend a gala in Austria.

We've confirmed Kaitlynn and Brody never followed up to get a marriage license here in the States ... meaning they never had a legal union.

Seems Brody is already fully embracing life as a bachelor, recently hanging with his boys for a night out on the town. You'll notice ... the wedding ring he slipped on at his "wedding" is no longer on his finger.