"After completing the quest http://www.uesp.net/wiki/Skyrim:Beyond_Death from the dawnguard side, the player can ask Serana to marry them and she will ask the player "Is that why your wearing an amulet of Mara?" after that she will say that even walking near a temple scares her, and will refuse to marry the player until they kill her father, and until then when ever asked "Have you ever thought about marriage?" she will respond with "I think we've talked about that enough, Come on now."

Just read this on the UESP, i suspect this is a troll as people have been complaining non stop about this.

Edit: Changed font colour.

nvrm. I really want to marry her cuz she's perfect for my vampire character. She's kinda hot too.

Todd be trolling us.

Sorry about the font i don't know why it appear black.

I want to marry her!!! HOW THE HELL CAN I KILL AELA?!?!?

Maybe you just need to do something special or not do something, Remember people thought Taarie was bug for the longest time and she wasn't. Won't know for sure until the PC version comes out and were able to Rip apart the code.

You can just turn your spouse into a vampire via the mission called "the gift"

Use the http://www.gamesas.com/forum/196-dawnguard-cheats-hints-and-spoilers/ for this kind of topic.