They first went public with their romance in November 2019.
And things seem to be going from strength to strength as they made a rare appearance together at the 2021 National Film Awards in Porchester Hall, London, on Thursday.
The Gavin And Stacey star, 42, looked smitten with his set designer girlfriend, 27, as they held hands while posing for pictures on the red carpet.
Sweet: Mathew Horne, 42, made a rare appearance with girlfriend Celina Basisli, 27, as they held hands while on the red carpet of the 2021 National Film Awards in London on Thursday
Mathew put on a dapper display in a black suit jacket that he donned over a crisp white shirt and black trousers.
Celina, meanwhile, looked stylish in a blush pink dress that had a ruffled, tulle skirt, which she paired with sparkly socks and fluffy slippers.
She styled her golden locks into loose waves that cascaded over her shoulders and accessorised with a black headband.
The happy couple made sure to stay safe amid the coronavirus crisis by wearing white face masks while at the event.
Sharp: Mathew put on a dapper display in a black suit jacket that he donned over a crisp white shirt and black trousers
Chic: Celina, meanwhile, looked stylish in a blush pink dress that had a ruffled, tulle skirt, which she paired with sparkly socks and fluffy slippers
Mathew claimed the award for Best Actor in a TV Series for Gavin & Stacey during the night and seemed very pleased as he posed with his gong.
Rowan Atkinson and Kate Beckinsale were also among the winners at the National Film Awards UK.
Rowan was honoured with the Global Contribution to Motion Picture and Lifetime Achievement Award for his legendary career on screen.
The Johnny English star said: ‘I would like to thank the National Film Academy for this special honour and all the film fans who have supported my career for so long.’
Stylish: Celina styled her golden locks into loose waves that cascaded over her shoulders and accessorised with a black headband
Success: Mathew won the award for Best Actor in a TV Series award for Gavin & Stacey
While Kate took home the Best Actress gong for her role in the movie Farming.
She said: ‘Thank you for voting me Best Actress at this year’s National Film Awards UK. I wish I could be there to pick it up in person but unfortunately the COVID quarantine is stopping me from being able to do that.
‘I want to thank all of our cast but particularly Damson Idris, who was the sun around which everybody orbited as is the most brilliant actor.’
Other winners included Vanessa Redgrave, who claimed that Outstanding Achievement Award – a surprise accolade that was bestowed on her for her decades of contribution to the world of film.
In July 2019, Mathew was first seen kissing set designer Celina in Burger King during a night out in Wales, while they were busy filming the Gavin And Stacey Christmas special.
Celina, who graduated from University Of Arts London with a first class degree in set design, lists the Gavin And Stacey special on her online CV.
With the kiss, he appeared to confirm his relationship was over with Casualty actress Evelyn Hoskins, who he proposed to in October.
Mathew and Evelyn were rumoured to have split in December 2018 but neither have confirmed this is the case.
Following the kissing pictures, a spokesperson for Mathew has since told MailOnline: ‘Mathew and Evelyn separated amicably in October 2018.
British actress Evelyn – who is most well-known for playing on-off character Shona Wark in Casualty – has never previously shied away from gushing about her man.
Mathew previously sparked rumours that he and Evelyn had already tied the knot back in August 2018, after he sported a ring during an appearance on This Morning.
The actor was also previously romantically linked to singer Laura Marling nine years ago.
Splitsville: In July 2019, Mathew was first seen kissing set designer Celina in a Burger King, which confirmed the end of his nine-month engagement to actress Evelyn Hoskins (pictured)
2021 National Film Awards UK: The winners
Best Actress sponsored by GLabs
Kate Beckinsale (Farming)
Best Actor sponsored by Eden Perfumes
Adewale Akinnuoye-Agbaje (Farming)
Best Newcomer sponsored by Urban Veda
Best Actress in a TV Series sponsored by Initio Parfumes
T’Nia Miller (Years & Years)
Best Supporting Actress sponsored by Storm Label
Gemma Jones (Rocketman)
Best Actor in a TV Series sponsored by RICH Prosecco
Mathew Horne (Gavin & Stacey)
Best Supporting Actor sponsored by Heart of Suffolk Distillery
Khali Best (Blue Story)
Best Drama sponsored by Dechavel
Best TV Drama Series sponsored by Heineken
Outstanding Achievement Award sponsored by Initio Parfums
The Haunting of Borley Rectory
Best Independent Film sponsored by Gen Nee
Rise of the Footsoldier: Marbella
Best Screenplay sponsored by Samantha Siu Inc
Liam Gallagher: As It Was (Liam Gallagher, Gavin Fitzgerald, Charlie Lightening)
Best British Film sponsored by Eden Perfumes
Lynn + Lucy
Eaten by Lions
Best Animation Film
A Shaun the Sheep Movie: Farmageddon
Outstanding Performance sponsored by Chloe…With Love
Louis Ashbourne Serkis (The Kid Who Would Be King)
Best Feature Film sponsored by Storm Label
Lucas & Albert
Best Director sponsored by MONPURE London
Shelagh McLeod (Astronaut)
Ged Doherty, Elizabeth Fowler, Melissa Shiyu Zuo (Official Secrets)
Best Film Distribution Company
Best Film Production Company
Best Foreign Language Film sponsored by Irene Kol London
Jessica Forever (France)
Best International Film
The Boy Who Harnessed the Wind