Offset might've spent Valentine's Day with estranged wife Cardi B ... but it seems he's enjoying some alone time on the weekend -- gambling away down in Florida.

We got video of the rapper at the Hard Rock Hotel & Casino in Hollywood, Florida playing cards on his own Saturday night.

Eyewitnesses tell TMZ ... Offset played for about two or three hours, tossing down an average of between $1,500 and $2,000 a hand.

We're told he wasn't playing a high-limit table ... but, we're told that didn't stop him from dropping a few grand -- pretty obvious from the frustrated expression on his face.

Offset lettin' it ride comes at the end of a pretty noteworthy week in his love life ... we broke the story, the estranged couple grabbed dinner at Carbone in Miami Beach on the day of love -- trying to stagger their entrances to avoid drawing attention.

Didn't exactly work out ... the dinner caused a flurry of speculation about the estranged couple -- who've admitted to getting it on recently -- but, as far as we know, the pair aren't back together.

The couple announced they were splitting up at the beginning of December, but they've seemingly kept things amicable -- spending major holidays with the kids. So dinner on V-Day sans children raised some eyebrows.