Sydney Sweeney's ex-fiancé Jonathan Davino is no longer engaged to the actress and their wedding's been called off ... but at least he's got her dog to keep him company.

Jonathan was spotted Tuesday for the first time since the news broke that the couple's been separated since January ... and he was walking her dog around the Bel Air mansion where they were supposed to live happily ever after.

Sydney's ex was all business as he fulfilled his duties at Sydney's property, which is getting some new construction.

Looks like Jonathan is loyal to a fault ... just like Sydney's dog.

We broke the story ... Sydney and Jonathan have been separated since January and will no longer be getting hitched in May as was originally planned.

Sydney's been living it up since the split ... splurging at the Beverly Hills Hotel with her girlfriends, taking the girlies to Paris Fashion Week and Africa, plus another tropical vacation.

Jonathan, meanwhile, looks like he's been left to look after Sydney's construction project ... and her dog.

SS and JD sparked dating rumors in 2018 and got engaged in 2022 ... but the good times are over.