Assuming you don't have kids, and your girlfriend is about the same age as you, you're combined quest for adventure and concubinal fidelity is... problematic.

Sure you love each other, but if there ain't no ring or fetus holding you together ( "Lemme go! Lemme go!) , life is sure to bring unexpected doubts (and benefits) to you both over that nine month period. And ten times as many the next time you leave for nine months.

And to be blunt, does she really trust you not to sow your wild oats in foreign pastures while the rain rains and the native girls dance? Because if she has even 1% doubt, then you must have at least 2% concern that she will voice those doubts to Antonio, the new olive skinned, long haired waiter at the coffee shop she goes to. He's a really nice guy and loves to listen.

Ya pays yer dime and ya takes yer chances.