The cheating partners might have lost the enthusiasm with their partners perhaps, because they are naturally inclined to be just that or because their partners might have grown cold toward them and have started to ignore them lately.
The handbook trusted by lovers to get valuable information about the 'ups and downs' of a relationship -
The Handbook of Cheating - has explained why
cheating partners cheat.
The Handbook of Cheating is 93-page book which explains a great deal about relationship issues.
It is available for download online for only $7.50 at
http://www.handbookofcheating.com/