There are different types of hepatitis. Types A and B could possibly be caught from another person's saliva. Hepatitis C can only be transmitted blood to blood. In other words, they would have to be sharing blood in a way that gets the virus from an infected person into the recpient's bloodstream.
If Bear has casual sex with random people and I'm willing to bet he does, he's more likely to get an infectious disease that way.
I'm not condoning the spitting, just pointing out that Hepatitis C can't be spread through saliva.
How many strangers do you think he"s snogged? If you take his word for it, he's always casting around for random bodily fluids.
And again, Aubrey was out of order, and BB would be criminally responsible if Bear caught something. They knew she had done it and could have prevented him consuming the tea and food.