They're back ON! Ben Affleck and Lindsay Shookus reunited for Oscars weekend and Ben looks ECSTATIC!

The Saturday Night Live writer arrived to Ben's home Saturday afternoon, straight from LAX with luggage in tow, and by the evening, she and her actor beau were off to sushi hotspot Katsuya for a romantic dinner.

We already knew the two were seeing each other again, following Ben's stint in rehab, the demise of his brief relationship with Playboy model Shauna Sexton, and his return to health ... but now they're taking it to the next level!

HILARIOUS mistake by Ben on date night, though ... check it out!