As the title states, I did what I didn't think could be done, I marred Serana. Due to space constraints I'll just list the relevant facts.
First off, my character is an Imperial male named "Drakulya" and before I installed Dawnguard I was already a vampire and also the "Listener" of the Dark Brotherhood. I'll also note that I have not yet completed the first main quest - where you retrieve the dragon stone, thereby bringing about regular dragon encounters- so dragons are not yet in the game. I have Heathfire and Dawnguard installed, but haven't downloaded DB yet.
I completed the Dawnguard questline a while ago now, but I remember answering some of the answers I gave to Serana and will list them here, in case the conversational responses matter.
When she asked if I enjoyed having her around I said "Yes"
I said "No" to having a wife and when she asked about my relationship with my parents I said that I hadn't seen them for a while and it was best that way, to which she insinuated that she knew how that felt. ( I can't recall her exact response though )
Since completing Dawnguard I've yet to have her wait or dismissed her, so she's been a constant companion for some time now and I never gave her flak about being a vampire.... but I believe the most telling point is that I didn't put the amulet of Mara and talk to her until dusk on day 666, just north of Riften. ( I'd tried before but when she declined I reloaded an earlier save as and continued the game as if I'd never proposed ) I'll recount as close to verbatim as I can what happened. (I saved and reloaded/ played several times so I could be as accurate as possible )
"An amulet of Mara? On you? Now there's a sight I thought I'd never see."
Upon clicking on her, two dialogue options appear-
A- "Eternity can be lonely expanse of time, wouldn't you agree?"
B- "Don't presume to understand my hearts intent, or be the focus of it!"
Choosing A brings about an Oscar winning performance from whoever the voice actress for Serana is, as she infused a lot of emotion in her dialogue-
"I would. You know, when you've lived as long as I have, you'll have seen men and women of all kinds, heroes of old and scholars whose intellect couldn't be measured.... many have sought my company, but I refused them all, knowing that time would first claim them and then eventually my memory of them. But at no time in all the history of Tamriel have I ever encountered..... you. My father said our companionship would not withstand time, but the place I have for you in my heart tells me otherwise. Is this mad affliction, this curse mortals call love something I suffer alone?"
A- Love isn't a curse Serana, its as treasured as our time together, may it never end
B- I'm sorry, I will never love you
Choosing A brings-
"Then let us experience the unraveling of time together and let our love be a final defiance to my father!"
Then Maramal appeared and said
"When Dinya insisted I come here, that her dream of two creatures of darkness being redeemed by the light of Mara's love was nothing less than a vision granted her by Mara herself... well, even I was skeptical, but here you stand, a miraculous testament that mother Mara's love truly knows no boundaries! Do you wish to be pronounced married?"
Serana will say yes, and Maramal will say that under the authority of mara, the divine of love, we are married. He then gave the two "Bond of matrimony" rings.
I've searched the internet and believe I may actually be the first person to have discovered this, so I will provide what information I can... I'm going to see about trying to upload something to youtube because I'm sure there will be a lot of skeptics... in the meanwhile I'll answer what questions you might have.
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The world is a dark place.....