I agree there is a fine line, but your missing the point, those things you mention are not consensual, sex is though. It depends on the people involved, if you cant settle for a once off lustysex session with another person that isnt a significant other and walk away then, yeah dont do it. if you can have the fun without the desire to stray from your significant other then work away I say. best of both worlds and both people will be more happy as a result and will actually strenghten a relationship as long as there isnt envy on the other side. women want a provider [forgive the stereotypical outburst there and understand the concept of paraphrasing please b4 ou jump down my throat] for when they have kids, and want to keep him around to ensure the families well being long term, but if they had a parrtner who a) understood that he has responsibities and b) its lust not love and not worth breaking homes over, and themselves a) hey he has his natural jollies our family is strong, I trust he wont stay strayed with her, he provides for my kids and me and he is still the alpha male getting to have his natural fun and Im ok with that.
tbh I blame religion for all this namby pamby view of families. one look at any nature program with lions will show you this [no those two other lioness' are not the other lioness sisters they are just other random mates he found and sheltered ect do you honestly think they went a found out the dna of them all :s, think about it