That's not literally true, of course: you can't marry a sword in any duchy of the realm, no matter how persuasive it is. Avella and Swift are in a committed long-term relationship, though, and all their friends accept it.
The legend is that Swift was once a man, a mighty warrior who did battle with a great evil, and whose soul sought refuge in his shattered blade as foul magics corrupted his body. This is also wrong in some important ways, but she doesn't usually clarify things because "dark magic transed my gender" is much easier for most people to handle.
