There's no one night stands here. The two of you have been involved in a relationship - what manner and definition, of course, is subjective - for a substantial (again, subjective and dependent on you) amount of time. But for whatever reasons, purposeful or not, you haven't had sex. Regardless of how that makes you feel, it changes tonight. You're taking that HUGE step and are going to sleep together. Finally, you may say. Or are you nervous, because maybe you haven't done this before and this could change everything? Are you suitably aroused? Suitably scared-oused? Ready to show them how much you love them?
Who knows, you may just be ready so sexually frustrated that you're ready to screw their brains out and break this vow of chastity that's been hanging around your little twosome. Anyway, ready or not, here you come.