I think it's a one-time compulsion. In fact, this is probably what Klaus uses to 'deepen his hold' on Stefan--by showing Stefan that he can make his worst nightmare come to pass at any time.

I think that by 'trying to reach Stefan' the synopsis is more along the lines of trying to get through to him, not location-wise. I'm fairly certain Stefan and Klaus are back in Mystic Falls for good now.

As for the 'why'--it's because Elena loves him, and wants him back, and is willing to do anything to get him back. Him biting her isn't going to change that(though I'm sure it'll traumatize Stefan to the point he really tries to push her away).Though I have a feeling she's going to go to lengths that not many people are very happy about--especially Jeremy if the synopsis is anything to go by.