I dont think that she necessarily has to be in love...but just to fill an emotional void.  But it almost always has to do with her not getting something at home.

 

and the guy will cheat because its there...he's almost always gonna leave it at that.  They will get nothing more out of it than sex.

 there are a very few who can think like men and just use them for sex...

but in most cases its because something is missing at home.

 

whether it be there is no more passion, he's not paying enough attention to her or something...but its almost alway emotional.