As for the SEX part, humans can be fickle minded, men or women, that's very natural. Example of sex hungry man is Doenitz I think

. Of course there are also civilised, sensible men who knows sex is not everything in life, or else we would be hamsters.
Why men are like that? We're made like that.
Men of the human species, can be said as fickle minded as well as loyal comparing to chimpanzees or mountain gorillas.
How I know? The physical differences of the three species says so, that is:
The size of the testicles!

The mountain gorillas have the smallest testicles compared to one of humans and chimpanzees, because they have only one soul mate throughout their lives. So males are loyal, and do not need so much sperms to compete with other males.
Chimpanzees on the other hand, the females are fickle minded and mate with different males at a go. Hence males have to have larger testicles, more sperms to compete with other males.
So as you can see the two sexes plays the game.
For humans however, our testicles size are somewhere in between of gorillas and chimps. Men and women of the human species not are loyal yet not fickle minded.
So the conclusion: Men not not always the only one hungry for sex but sometimes women too (don't blame it all on men, that's why we have gays as well as lesbians in the society).
So you have to judge for yourselves who's loyal or not.