Amber Rose Divorce ... She Says Wiz Khalifa is a Serial Cheater

8:50 AM PT -- Amber Rose took to Twitter Thursday morning and addressed all the cheating rumors, writing, "Please stop with the fake stories. I would never ever ever cheat on my husband in a million years I think u guys know this.....Unfortunately my now ex husband can't say the same."

Amber Rose has filed for divorce from Wiz Khalifa because she's convinced he's been a serial cheater for months ... making lame excuses that just don't hold water.

TMZ broke the story ... Amber filed legal docs Wednesday and it's a bitter break-up, with each accusing the other of cheating.

Sources connected with Amber tell TMZ ... since the beginning of Wiz's tour in July she strongly suspected he was stepping out.

Amber's telling friends ... she wanted to join Wiz on the tour but he came up with a panoply of excuses, the most frequent of which ... she should stay home with their 1-year-old.

She also says he tried to show dominance by telling her he's the bread winner and he needed to be left alone to make money and she needed to stay home. BTW ... we understand that doesn't make a lot of sense, but that's what she said.

As we reported ... Wiz believes it was Amber who was cheating, courtesy of Nick Cannon, and she's throwing up allegations against him as a cover for her own misdeeds.

And Wiz has complained privately ... Amber is one big nag.