Board Thread:Skyrim/@comment-107.200.47.75-20150119072427/@comment-24329883-20150119073846

If you're playing on a console, then you will have to remain a vampire lord to advance in the Dawnguard questline as a member of the Volkihar clan. If you cure yourself and you still have some more main quests to do from the Volkihar, then they will prompt you to get re-infected by either Harkon or Serana. The opposite is also true if you want to play as a member of the Dawnguard, whereby they will force you to get cured of vampirism.

The Volkihar vampires won't be hostile to you, but they will insist that you get re-infected before they help you out or give you quests.

If you're playing on PC, you have a bit more freedom to play around if you're willing to use console commands and/or download mods.