If you decide on Europe just make sure you sleep as much as you can on the airplane. The time frame you are talking about sounds a lot like the schedule we work, and you will be tired. The big difference is that you will be with someone special and on a very special trip so you'll probably have a lot more energy.
A lot of us do several trips back to back so we're usually wiped out, just doing the one probably won't be too hard. For my non-airline friends that think my job sounds so glamorous, I just tell them that it's a fancy place to sleep. U.K. and Ireland are the shortest distances if you do decide on Europe, and only 5 hours difference in time zones.
Wherever you go, have a great time!!