Marriage is changing and so is monogamy. While it is a viable option for some, it clearly isn't for everyone (just look at the success of Ashley Madison - a site for cheaters). Patricia Johnson and Mark Michaels are the authors of Designer Relationships where they explore non-exclusive relationships, emotionally exclusive relationships, kinky relationships and so much more. Regardless of the relationship, monogamous or otherwise, the success of the relationship is based on trust and transparency.

Website: www.MichaelsandJohnson.com 

Books: 

Designer Relationships 
Great Sex Made Simple