The "problem" here comes from YOUR view, of what a relationship SHOULD be.
You mention how fake it is on MTV and trhe like, but it's not fake, it just doesnt fit YOUR perception (based on of course your parents standards, media, and largely societies standards of what is considered "normal") of how they should be- Neither view is correct, they are different, nor are they wrong.
What it boils down to in the end are EXPECTATIONS.
..Should you even be EXPECTING that since someone is in a commited relationship that they wouldn't cheat?
Second, For a female, how much of the act of cheating is a cognitive one?,.. not much I'll t ell you. Yes, they KNOW they are, but just like you slept with her the first time and she told her friends "It just happened", means she was lead emotionally.
For a male, cheating doesn't carry the same weight, as in general, it is purely a physicial act, with NO emotional investment.
Conflict arrises, when you try to put "contractual" paramateres around a purely primitive emotional/ physiological responses.
THINK back when there were no marriges, You could do whoever, whenever, and jelousy was strictly to maintain breeding possibilities.
There was no expected loyalty. Biologically, men are designed to spread their seed basicly whenever, we have built in diversity needs as well (which can and have been tamed over the years to some degree).
Certin woman have greater degrees of primitive-like behaviour, where there reality is lead mostly on emotions, which, as you know, change ALLLLLLL the time
Thats how she can screw you, go to a party and screw this other guy that turns her on, and come back to you tell you she loves you, while whole hearted beleiving that, becasue at that time, she does..
Anyways, basicly, the only security is Attraction and Love, TOGETHER.
Meaning, if you turn into a whiny lil biotch, she will lose attraction. If you fail to lead her, she will leave, if there is just someone better, old with the old and in with the new.
This has NOTHING to do what the media portrays, or current standardrs. This is strictly primitive, and you find a WAY to do it within the social constructs.
I whole heartedly beleive, and has been my expirence, that this underlaying factor is completely true. All other factors, such as "being someone's boyfriend" or marrige only act as a DETERRANCE to this, delaying, possibly eliminating infedility in men and women.
Your best tool is screening, and having realistic or NO expectation from the other person.
When a woman is really into a guy, she will be TOTALLY faithfull, and she stays. This, of course, is dependant upon the GUY, how HE acts/does/leads/...
The rules of nature also allow this to happen when one man, has multipule women.