Maybe wait until after dinner’s over?
Since restaurants are busiest during Valentine’s Day, the waiting staff doesn’t have time to eavesdrop on every conversation going on. It’s usually the outbursts that get the staff’s attention. So, as the OP was preparing to drop off the bill, he only caught the tail-end of the patrons’ conversation: “it’s over.”
The relationship was over, not dinner. They hadn’t paid a dime for their meals and drinks yet. So, out of spite, the guy told the OP to “split the check, right now.” If we were in his position, we would’ve totally fueled the drama by splitting the check for them.