Bethesda should have seen this coming come on... First it was Lydia and now Serena are among the few female characters flung at the player. But honestly Serena script sounds a little "lovey dovey" with the player. Lines similar to "He has done more for me then you did in centuries."
Ha that phrase isn't even scratching the surface.
If you choose any options that sound like you care for her, she gets all mushy on ya. I have been under the impression we would get the marriage option, since I'm still doing Dawnguard. Guess we don't =p