first filter;
Correct. It's literally life or death eventually.
Like you said, it functions the same way a STD does, so any sort of sex runs the very high risk of it being passed on. I assume protection helps lower that risk, but I can't give you a definitive answer. And a couple of years now? Maybe not quite that much. Time's also very weird, especially when you spend so much of it in Fillory (long story).