DeMario Jackson's Ex-Girlfriend Hates Him But Swears He'd Never Take Advantage of Drunk Corinne

DeMario Jackson's ex-gf -- the woman who exposed him as a villain on national TV -- is actually coming to his defense in the Corinne Olympios scandal ... but she has a strange way of doing it.

Lexi Thexton claims DeMario is nothing more than a "30-year-old man child" who parties way too much -- but also says there's no way the "Bachelor in Paradise" star would knowingly take advantage of a drunk woman ... as Corinne insinuated when she declared she's a victim.

For Lexi to say anything supportive about her ex is a big deal. Mind you, she also called him a "sh***y guy" who's completely self-absorbed ... among a list of other insults. She did offer a theory about what really happened with Corinne -- and strongly believes it's more about 2 people getting too drunk.

For non-'Bachelorette' viewers ... Lexi made a surprise appearance on the show, calling out DeMario for trying to woo Rachel Lindsay while still dating her. He got booted off the show that very same episode.