This is what I'm thinking: Bill gets captured, imprisoned, and tortured by someone who may have an interest in Sookie as a source of power to be used. That someone makes Bill agree to a deal: Bill will be freed from his captivity and torture if he commits to the task of helping Sookie develop her telepathic abilities which have powerful lengths she hasn't covered yet and then deliver her to that person. After reuniting with Sookie, Bill keeps the deal a secret from her while trying to figure a way out of it. It won't be until near the end of the season or the season finale that Sookie finds out the truth.
