Thomas Barrow in Downton Abbey fanfiction is often a complex character. He is sometimes portrayed as a sympathetic figure, despite his flaws. Fanfiction writers might explore his inner turmoil, like his struggles with his identity and his place in the strict social hierarchy of Downton. His relationships with other characters, such as his interactions with the other servants, are also rich areas for exploration in fanfiction.
Another theme is his relationships, especially romantic ones. Since his romantic life was not fully explored in the show, fanfiction fills this gap. Writers might pair him with other characters, either from the servant class or even from the upper class, creating interesting power dynamics and stories of forbidden love.
There might be. You could also check some dedicated Downton Abbey fan forums. Sometimes fans share their own written fanfics there, including those with gay themes related to Thomas. However, the quality can vary greatly, so you may need to sift through a bit to find the really good ones.
Archive of Our Own (AO3) is a great place to start. It has a large collection of fanfics, and you can easily search for Downton Abbey related ones with a gay Thomas theme. Just use the search bar and type in the relevant keywords.
Definitely fiction. Downton Abbey creates a fictional world with made-up characters and events, although it may draw inspiration from historical periods and social contexts.