Your sweetheart is a stag...
No, I don't mean THAT kind of stag, come on!
Your sweetheart REALLY is a stag, cute, cuddly, antlers, fur, you name it...
He is human too, but he is in stag form for 1 year and a day for ... well, reasons. And if you wonder why, well read the Milesian Accords books 1 to 3, it shall give you the perspective.
And you being the cute, lovely, err badass dragonslayer girlfriend, don't want anything to happen to him. And so, well, you accompany him for his stag year, doe-eyed and all that.
If it were THAT simple... Course it's not. Want to know more? Read the book, you won't be disappointed.