I Gave In

My wife and I recently had a baby and we also have a six year old girl. My wife's cousin Christine is a professional childcare worker so we hired her as a full time, live-in nanny. She stays in the spare bedroom downstairs and she's great with the kids so we pay her pretty well.
As of late, I have found myself growing more and more sexually attracted to Christine and having fantasies about fucking her. She has not given me any signs or looks anything. It's all in my head but she's a carefree, attractive young woman and it drives me nuts.
Last weekend my wife and the kids were out of town visiting her folks and I came home late from work to find Christine having drunken sex with some dude in the livingroom. She was really drunk but still managed to be super embarrassed. I don't think she knew the guy all that well either because when she kicked him out, she couldn't remember his name. She then spent half the night throwing up in the guest bathroom. The next morning, she apologized and begged me not to tell my wife. I promised not to but part of me contemplated blackmailing her into doing stuff with me. I didn't do it. But it really crossed my mind for a second. It's been about a week and she's still awkward around me. And I get hard thinking about her bouncing up and down on that dude. I think about it constantly now