Lea Michele is standing by her man ... TMZ has learned the "Glee" actress has decided to keep dating new BF Matthew Paetz because she's convinced he's no gigolo -- he just coaches 'em.
Sources close to the couple tell us ... Lea was PISSED after we broke the story about Paetz's involvement with Cowboys4Angels -- a website that offers male "companionship" -- and confronted him about it.
We're told Matthew copped to going on a few dates with female clients ... but told Lea he only did it as research -- so he could understand what the gigolos go through and coach them through it.
This guy is good ... 'cause we're told Lea actually bought it, and Matt promised he'd never do it again.
Our sources tell us Lea's not getting the full story ... because Paetz has had more than just "a few" dates while working as a gigolo for almost a year.