Cassie Forced to Smile Through 2018 Club Gig with Diddy, Months Before Split

Cassie was pushing through with Diddy during their tough years together ... making it seem like all was well in their relationship while onstage with him in Dubai -- before finally calling it quits.

TMZ obtained this clip of Cassie playing along with Diddy during his first-ever Dubai performance in April 2018, and you can see she was doing her best as the rapper performed "I Need a Girl (Part 2)" at the opening night of the now-closed Gotha Nightclub.

On the surface, the pair looked happy, with Cassie glowing as she busted out some moves. She got up close to share a hug with him before making her move way to the edge of the stage.

You can also spot his sons, Christian and Justin , joining the fun in the video ... we're told Diddy even invited Christian onstage so he could belt out his new track at the time, "Love You Better," which he put out with Chris Brown .

A few months later, in October, Cassie's rep confirmed she and Diddy had broken up -- and had been for months. So, it seems their split happened not long after this serenade.

Of course, now we know their relationship had been tumultuous -- something made painfully clear by the 2016 hotel surveillance footage of the disgraced rapper beating her, which surfaced this year.

CASSIE THROUGH THE YEARS

Click Image to Open Gallery

While Cassie now enjoys her freedom from the relationship, Diddy’s facing a much darker reality -- sitting behind bars with a slew of allegations hanging over him as he awaits his next court date on October 9.

We reached out to Cassie's attorney, Douglas Wigdor , and Diddy's reps ... so far no word back.