Its supposed to satisfy many different needs. If either isnt getting what they want of need, its only natural that they will at least think about going elsewhere for it, or actually take that step when the opportunity is presented. We are animals, after all.
Even though I myself am a full monogamist[my womanizer father 

]. I believe that a woman deserves a man who can satisfy her needs and desires and that if she isn't satisfied should be allowed to proceed on to a man who can. To me its nothing about sexuality being animalistic but rather simple biological rights.
Also I believe that sex doesn't have to be animalistic. Sure it is driven by primitive instincts. 
But it can be done almost like an art and my 
own personal principle is that it should be reserved between those who are in love. For I hold it to be an exclusive act that lovers perform with each other, which both; gives an incredibly euphoric sensation and due to this being as such, reserve the performance of it with each other and also one that strengthens and deepens the bond that they have between them and increases their attachment over each other.
That's why I want to become an ascetic unless I find the right woman.