Demi Moore's Rumored Boyfriend -- WE'RE NOT DATING

Demi Moore's still a single woman ... despite reports claiming she's moved on from Ashton Kutcher with a 26-year-old art dealer -- so says the rumored "new man" himself.

Vito Schnabel -- the son of director Julian Schnabel -- was out at an art event in Miami last night when he was asked if there was any truth to the rumors he's dating 50-year-old Demi. Vito responded, "No. Nope."

But just hours later, Vito and Demi were spotted together at some Chanel party -- along with Lenny Kravitz and Stacy Keibler -- and "Demito" reportedly even MADE OUT.

So we gotta ask ...