In the episode "The Green Muse", Dr Ogden and Detective Murdoch end up making out and they nearly go all the way. Julia stops it just on time with asking William if he has any "precautions" or prophylactics. Obviously, he doesn't as he didn't know he would be needing any, not to mention that contraception methods are illegal. However, it's later revealed that Dr Ogden is barren and she couldn't conceive anyway, so why would she ask for condoms? The brilliance is in her knowing that sex would be a step much further out of their comfort zone. Even though they are both ahead of their time, sexual relationship before wedding would be too much or going too quickly.