I've been with the boy for coming up to 19 months and been living together for 9 months. We have sex whenever I want to; up until ~2 months ago that was pretty much every day. But recently, with his finals, my first set of exams i've been serious about, and other problems, money etc. I've just not been in the mood so it's once every few days. My lack of interest has now turned into a game where I'm seeing how long he'll hold out without sex until he wants to talk about it to try and gauge how big a deal it is for him. Poor guy.
When it's a LDR though, as it will return to being next year when he's working in London, it'll be a case of basically spending the whole weekend in bed.
If you're worried that you don't have sex often enough, just initiate it more often.