'Housewives' Star Apollo Nida -- There's NO Proof I Cheated

"Real Housewives of Atlanta" star Apollo Nida is NOT a dirty, cheating scoundrel ... so he says.

There have been a slew of stories circulating he's guilty as charged. But Nida tells us ... there's a perfectly good reason why he was spotted in South Carolina on Valentine's Day weekend with another woman -- NOT his wife, Phaedra Parks.

Apollo says the woman was his friend's sister ... a bartender at the club where he was paid to appear. Nida says it's all perfectly harmless ... the majority of his fan base is made up of women ... so naturally that's who he parties with. He insists he's 100% faithful, and there are no sex tapes, no naked pics, no pregnant baby mama to suggest otherwise.

Apollo actually has much bigger fish to fry. He's facing federal charges for bank fraud and identity theft.