You know what's not normal? Monogamy.
The want/need to reproduce is in the DNA of every living organism, however, with biological and hormonal change that want/need may dissipate.
Monogamy was forced upon us at some point in time and now it's accepted. I believe this to be a large part of why people cheat, I know of people that are very happy with their relationships on all levels yet still feel the urge to be with someone else purely in a sexual nature, does that make them a bad person, or is it just the human condition?
How many of you that are in happy healthy relationships, have seen a person you find sexually attractive (not your partner) and thought to yourself "hmm the things I'd do..." ??
Every single one of you! If you say otherwise you are lying.
In saying this, I am trying to illustrate my understanding for people who "cheat", in no way do I condone cheating and potentially causing a lifetime worth of damage to the other party.
I have never cheated, but have been cheated on, sure it hurt, and messed me up for a while, she was my first true love and she fooled around with a very close friend of mine, I'm not jaded, because of my open mind and realistic take on things I found myself talking to both of them about what happened and was able to analyse the situation and have an understanding of why it happened, which made it a lot easier to deal with. I think emotional cheating is far worse than physical cheating.
I have a fairly high sex drive, and I have spoken to my wife on multiple occasions about feelings that I have, I am one of the people I mentioned above, I love my wife, we are happy, don't argue a lot and when we do it's very civil, we have a great sex life and work well together to have our family succeed, but I'm still attracted to other women, if I could have my cake and eat it too I probably would, but that won't happen because she doesn't feel the same way as me and I respect that. Judge me, hate me, whatever, it just proves your ignorance to other peoples lives and situations.