Is it normal for men in long term relationships to want to have sexual relationships with other women? If a man who is married or in a long term relationship wants to have sexual relationships with other women, is this pathological, deviant, maybe even a disorder? Or is it part of normal and healthy male sexuality?
The issue here is 'normality' - normal is a shifting social construct, meaning that any answer concerning normal will be based on culture, and thus could change depending on the culture in context.  A better question would be, is it adaptive or maladaptive for the person in question.  

But I don't think that's what you're asking - (I could be wrong) it seems you're asking more about satisfaction of desire and whether a single partner can accomplish that.  

Let me flip the question around:  


  If a woman who is married or in a long term relationship wants to have sexual relationships with other men, is this pathological, deviant, maybe even a disorder? Or is it part of normal and healthy female sexuality?


We can flip the gender pronouns - but in doing so, we notice an underlying assumption of male promiscuity in the original question (likely related to the idea of 'spreading seed' or a belief in a biological imperative to have as many children as possible (if this is actually true, why aren't all people constantly having children?  I'm not saying it's not true; I'm saying it's much more complicated than that)).

Getting closer to an answer, let me pose more questions:


Does a happy/successful/[insert judgment function here] relationship require that both partners be satisfied in all of their desires?  

-- or --  
Does a happy/successful/[insert judgment function here] relationship require that both partners learn how to control their own desires instead of being directed by them?


But that's a false dichotomy; the answer will never just be one or the other.  A successful relationship will, first and foremost, involve communication.  If you can communicate your desires with each other, you can both, jointly/together, pursue a sense of satisfaction (or a sense of control over that desire).  

But not being able to communicate dissatisfaction is itself a sign of underlying problems in a relationship.