@aidan,
Yep, that's what I was thinking, too. This is obviously highly anticipated (six months in advance...?!) and things may well progress further and faster in that situation than you expect.
Even if you think now, "No, I'd never do that," that's not how it tends to work. There have been studies about how different our brains are in cold states (sitting in front of a computer) and hot states (pressed up against a naked girlfriend, with no parents around). The studies often have to do with exactly this situation -- people who plan to avoid having sex but then get themselves in "hot state" situations.
Can get the studies and stuff if you're interested. My advice is in two parts:
- If you really, really feel strongly about not having sex, don't put yourself in that situation.
- If you go ahead and do it anyway, be sure you have a backup plan available (i.e. condoms).