Andy Cohen is reacting to the Jill Zarin firing ... and he says he knew it was bad when a fabrics company with a family connection to Jill came out hard against her on social media.

The Bravo host addressed Jill's recent firing from the E! reunion show "The Golden Life" on his radio show ... and he says what sent things over the edge for him was an Instagram post from Zarin Fabrics.

As you know ... Jill got canned for her controversial comments on the Bad Bunny performance at the Super Bowl LX Halftime Show. Some folks took her comments on Bad Bunny singing in Spanish as racist. She also lamented a lack of white people in the production.

Zarin Fabrics -- a company owned and run by Zarin's stepson, David -- posted her headshot on IG and struck a big, red X over her face ... and explained in the caption they distanced themselves from Jill.

Andy says Jill had been singing Zarin Fabrics' praises in the weeks leading up to the Super Bowl ... so to see the company turn on her really struck him.

When Zarin Fabrics posted, that's when Andy knew the walls around Jill were crumbling ... and he says he will never get over the post.