Three books:
To deal with the emotional cheating: His Needs, Her Needs - http://www.amazon.com/His-Needs-Her-Participants-Guide/dp/0800721004/ref=pd_bxgy_14_img_y
To deal with the sex: You still give me butterflies - http://www.amazon.com/You-Still-Give-Me-Butterflies/dp/0615376630
101 Nights of Great Sex - http://www.amazon.com/101-Nights-Great-Sex-Anticipation/dp/0962962872
The first book is going to discuss 5 needs of men and 5 needs of women. The sum of it is, she has a need that is not being met and thats why she is seeking it elsewhere. You can fulfill her need if you understand what it is.
The other two books are both split up into "his eyes only" and "her eyes only". They are exact instructions on how to set up a romantic night for you and your S.O. For example, a "his eyes only" might tell you to go pick up some message oil, make a mix tape, and buy candles, etc. Then give her a oily message. It's pretty detailed and sets up the whole thing to include anticipation. So early in the day she'll get a "butterfly" card that says something like "plan for some adventurous hands tonight, wear next to nothing" and all day she'll be wondering what that means.
They are essential books, I think they'll help. You two should read them together.