I think sex is far easier than driving. First, there is absolutely no risk - OP is going to have exclusive unprotected sex so she has nothing to worry about. Driving involves a huge amount of risk. So that is one thing that makes driving harder. Second, sex is simply between two people and driving involves all sorts of players whom you do not know and whose behavior you cannot predict. That adds another layer of complexity to driving but not to sex. Third, there are rules of the road but sex has no rules, which makes sex easier - you do not need to learn and memorize the rules (and apply them, too!). Fourth, I assume that OP and her future husband will have low-tech sex without toys, so their sex life would just involve human bodies while driving involves technology/machinery that has to be operated, adding yet another layer of complexity.

All in all, sex is far easier to pick up for a novice.