Best course of action is return it to the roman empire for now and ask for support from constantinople. He already got support from native. take it back shouldn’t be a problem in the future.
Hard situation...
No idea on how to solve it
The only thing to do is to break the promise
I really hope Antonius will be able to guarantee the people of this town protection in the mids of this civil war
The is no limit to brutality in war