After quite a stimulative day yesterday one of the things the group I was with talked about is fidelity in a relationship. It started as an outcry from a girl towards the men of the group on why are we such primitive pigs that we have to ruin everything nice by cheating.
When I asked her where does she thinks fidelity sprouts from, she couldn't really answer because she knew that romantic love didn't prevent her from looking around.
So, I explained... In bite size thoughts, of course.
~Fidelity comes from fulfillment of needs and from the dynamic energy that needs to be felt by both of those in the relationship.
Fulfillment of needs: If you partner fulfills all or more then someone else of your basic needs (mental and intellectual, physical and sexual, social and status) you really won't have a reason to look around with nothing else but the corner of your eyes (looking isn't cheating, it's just not polite when you are with your partner). If something doesn't satisfy your basic level in some of those fields, you will be looking for someone that might will.
This fact does have a subsection that I shall call marketing.
If your partner presents false values to you that he/she doesn't have and you sniff that out you will deep inside feel scammed and will be more swift to break the fidelity idea into thousands of little pieces.
Ever changing energy: Change is constant, progress isn't. If you don't show an ability to change (preferably for the better) your partner will feel that and the energy of passion and love will just vanish over time and you will find each other just sitting in a coffee shop without anything to tell each other - and not in a "no words are needed" romantic way - just sitting there and being bored of each other.
After saying that to the most noisy girl, I asked her - So when you felt this faults from your partners, did you cheat on them. After an affirmative answer, I responded with another question - Is it possible that you gave out that vibe to the partners that left or cheated on you?
The rest is not important. Only these two fact and questions are.