Futamata hasn't revealed Uno's past to us yet, I decided to tell you the hypothesis I have regarding his past.
Uno was a child whose parents were very busy with work and they had absolutely no time for him. He suffered from attention deficit disorder and found solace in girls and gambling, and it was because of this that he started gambling. He may be in debt and that's what led him to have to scam women. He ended up in prison because he was denounced by the women he defrauded and also because he probably cheated at card games and deceived people until the police got interested. . I think that's the most likely past. But, of course, that's just a guess. His real past, we don't know yet unfortunately.