Congrats all 'round. Staying calm is easy if you've practised any of the Zen disciplines for about 20 years... No? Well, I've always found a wee bit (emphasis on the wee) of alcohol, like one glass of your favourite wine, helps. And there's Prozac...
More seriously now, if I may presume to offer some advice from the perspective of my (ahem) ancient wisdom... I've said something similar before somewhere on these boards, but it bears repeating:
Obviously you know what it's like to be in love, or this wouldn't be happening. Sadly, you're not going to feel that way all the time. It takes too much energy, for one thing, and distracts you from other things in life that'll demand your attention. Ya gotta be friends, and I think it helps if you were friends first. When life together gets complicated and difficult--and it will, I promise--it's friendship that'll carry you over the rough spots and keep you together.
I speak from a nasty experience, but that was in another life... Look on the bright side: if you're friends as well as lovers, you'll never have to go through this again. Just get through it once, you'll be fine.