WWE's Seth Rollins -- Secret Breakup ... With Wrestler Girlfriend

Seth Rollins is officially back on the market ... 'cause the WWE superstar and his wrestler girlfriend are down for the count.

Rollins had been dating former WWE wrestler Zahra Schreiber since at least last year -- and stuck by her side after she was fired by WWE in August over anti-Semitic posts on Instagram.

But according to ProWrestlingSheet.com ... the two "quietly broke up last month" -- and she's already moved out their place.