Sam Asghari Believes Britney Spears was Cheating with House Staff Member

Sam Asghari is telling people he believes Britney Spears cheated on him with a staff member at her house, and engaged in other inappropriate sexual conduct as well ... sources tell TMZ.

Sources with direct knowledge tell TMZ ... Sam has claimed Britney asked at least one staffer to shoot video of her naked. Not only that, we're told Sam believes she hooked up with at least one of the male staff members working at her home.

As for how Sam supposedly knows -- our sources say he claims there's footage of Britney and the staffer together in a compromising position.

We're told Britney's in a fragile and hyper-sexualized state, and it's contributed to her dangerous decision-making ... making her a risk to her own safety.

Our sources say Sam acted as a crutch for Britney for a long time, but her recent conduct was too much. We've reported Sam has been over the marriage for a while now, and recent events were simply the last straw, leading him to file for divorce.

As we reported, Britney's now without a support system -- she's iced her family out, doesn't have real friends, and has now lost Sam. We're told there's serious concern from her loved ones, but at this point, there's not much they can do.