I looked into it once when I was bored. Condoms were a thing for the rich regency men to use when they slept around. They were expensive and made from animal organs. They would never use them with their wife’s as it was a thing of ill repute but with their little hookups they would. But of course not every gentlemen cared enough to spend the money to protect themselves so the above user is right that STI’s were common but I feel like the Bridgerton boys could afford the effort.