I don't think Anne is the dr that saw Gideon when he was little. I think Anne was just used as revenge to Dr. Lucas. The next book will have lots of answers (I hope so).
I think Magdalena went to see Eva to say more mean things to her, I am curious to know what Sylvia would say about that. There is no reason for Magdalena go look for Eva besides say things about Gideon and to try to keep them apart.
There is a good question about Christopher and Magdalena, I wonder about that too. Gideon keeps saying that Christopher wants everything that Gideon has, so maybe Christopher know Magdalena feelings for Gideon and knows that Gideon cares for Magdalena and uses her to get to him.
When Gideon tells Eva about Corine, he says that she was his first consensual sex partner, so I would say Yes, he was a "virgin"
My guess is that Corine was the one calling him, since he was expending time with her and giving her more attention. I don't think he knew about the police going there that night, he knew they wold eventually get to Eva.
Eva moved to NY because she wanted to start over far way from her past (I think) and before that she was in a bad shape, until she started therapy and when she started together better, she wanted to be somewhere she could feel safer, and also to be close to her mother.
Maybe Brett's band was on tour? Is the only explanation I can think about it, or he got to the party after Eva left.
I can't wait for the 3rd book....