If one feels such extreme guilt after cheating, why is it so likely to occur again?

Even if you feel guilty chances are the reason you cheated are still present. You might have cheated because you lack affection, or feel taken for granted. Maybe your spouse works all the time and never spends time with you or maybe they are cheaters themselves. All those are reasons to make someone cheat. You'll feel guilty but unless those problems are fixed, Chances are you'll cheat again.

Because the other person will never truly trust them again. Period. Therefore, they figure they might as well cheat again since they are already suspected of doing so. That's why if anyone cheats in a relationship even one time, the relationship is basically doomed.

Because there is a reson for it.
Why do women go thru labor and birth over and over even though doing so totally sucks?
Because there is a reason for it.
If someone was happy, and their needs were being met, they would have no reason to look elsewhere.

I agree with the "drug-addict" point of view. Every time it gets easier and easier. I say this because I am the other woman. I have seen the man go from extreme guilt to coming back to me. I know what I am doing and I don't need any one to tell me I am a, well what ever you want to call me. I feel like shit for doing this too, but as cliche as this may sound, I love him. There is guilt, and each time the guilt wears off faster and faster. Maybe like aniyodea said, the "cheater" should look into his/her relationship and see what is missing. Because something is missing if you are looking elsewhere.

The only way they would feel guilty is if they were caught. Then after that's over, it starts again.

guilt:

1. awareness of wrongdoing: an awareness of having done wrong or committed a crime, accompanied by feelings of shame and regret

2. fact of wrongdoing: the fact of having committed a crime or done wrong

3. responsibility for wrongdoing: the responsibility for committing a crime or doing wrong

http://encarta.msn.com/encnet/features/dictionary/DictionaryResults.aspx?refid=1861615755

guilt (FEELING)

a feeling of anxiety or unhappiness that you have because you have done something wrong, such as causing harm to another person

"He suffered such feelings of guilt over leaving his children."

http://dictionary.cambridge.org/define.asp?key=34902&dict=CALD

a feeling of responsibility or remorse for some offense, crime, wrong, etc., whether real or imagined.

http://www.infoplease.com/dictionary/guilt

(informal) A guilt trip is a strong feeling of having done something wrong in a particular situation

If someone has a guilty conscience, they are unhappy because of something they feel they have done wrong.

http://dictionary.cambridge.org/define.asp?key=guilt*1+0&dict=A

Feeling of responsibility for wrongdoing

http://www.allwords.com/query.php?SearchType=3&Keyword=guilt&goquery=Find+it%21&Language=ENG

A feeling of regret or remorse for having committed some
improper act; a recognition of one's own responsibility
for doing something wrong. "Depression is often rooted in
guilt which has not been dealt with in an appropriate
way." "Guilt is a natural and appropriate consequence to a
wrong action."

http://www.freedictionary.org/?Query=guilt

a. Remorseful awareness of having done something wrong.
b. Self-reproach for supposed inadequacy or wrongdoing.

http://www.thefreedictionary.com/guilt

Subjective feeling of having committed an error, offense or sin; unpleasant feeling of self-criticism. These result from acts, impulses, or thoughts contrary to one's personal conscience.

http://cancerweb.ncl.ac.uk/cgi-bin/omd?guilt

a strong feeling of guilt. "I'm on a guilt trip about not visiting my parents often enough."

http://idioms.thefreedictionary.com/guilt

Traditional Japanese society and Ancient Greek society are sometimes said to be "shame-based" rather than "guilt-based" in that the social consequences of "getting caught" are seen as more important than the individual feelings or experiences of the agent. This may lead to more of a focus on etiquette than ethics as understood in Western civilization. This leads some to question why then we would adapt the word ethos from Ancient Greek when their norms are so different from ours.

Psychopaths typically exhibit a "lack of remorse or guilt" in the face of wrongdoing. This is seen by psychologists as part of a lack of moral reasoning in comparison with the majority of humans, an inability to evaluate situations in a moral framework and an inability to develop emotional bonds with other people.

Guilt, in psychology, a term denoting an unpleasant feeling associated with unfulfilled wishes. Sigmund Freud initially contended that sexual drives produce sense of guilt in the superego, the moral conscience of the mind. He later maintained, however, that guilt was associated with aggressive impulses. Freud felt that guilt was often confused with remorse, the former being an emotion signaling the presence of aggressive wishes, the latter a self-imposed punishment which occurs if the aggressive wish is fulfilled.

Guilt is part of awareness. It makes us realize what we have done.

Because the thrill of cheating is much more powerful than you remembering the guilt that you felt the last time you cheated.

If your going to cheat you might as well be single, no guilt. problem solved. Cheaters........tisk tisk show some respect.

well sometimes cheating (like stealing, killing or doing anything wrong) can become addictive, especially if you dont get caught because it is a "quick fix" so to speak. look at it from a drug addicts point of view: some one or something introduces him/her to drugs. they try them and become addicted. eventually guilt and/or denial builds up but that person cant resolve the problem because he/she becomes accustom to doing it even though its wrong so whats the quick fix for it? they continue to use drugs knowing that its wrong but unable to stop because they are too weak to do so without serious help. just replace the drugs with cheating, and you get a pretty good idea of what im trying to say. and the most guilt after cheating comes from the first time it is done. after the first few times the guilt pretty much wears off and cheating is done without thought or remorse. i have never heard of a person chronically cheating and feeling "extreme guilt" every single time they did it, because it would build up so much that either they would stop cheating, tell someone, get professional help, or their head would probably pop off holding all that "extreme guilt" inside. and the more likely it is to occur again, the less guilty the person feels about doing it......just like a drug addict.....think about that.

my guess would be, that feeling terrible about what you did already clears your conscience in a way. It's a way of "pay as you go". You cheat - You "pay" by feeling terrible about it - you're ready for the next round.

It also never harms to look a bit more deeply into the relationship you're in, and try to recognize what's missing there that makes you look for it elsewhere.

Depends if you feel guilty cuz you know you did wrong - or cuz you were caught.
There's temptation all around us. We aren't immune to it just becasue of guilty feelings.
On a religious aspect, our whole life is a series of temptations that we have to overcome to show whether we choose God or the devil.
I also agree that once you do it - no matter how bad you feel after - it's easier to do it again.
I guess too, it could be dependent on the person's morals and how they value themselves and others...

maybe you are to perfect and you need to do something wrong some time!! then you can feel human again.
Maybe you are with the wrong partner in life!
maybe you are just more sexually active than your partner!
Maybe you are just human! they do that kind of things.

Its not always.
Sometimes its an isolated mistake.
I know that was the case with me.

because once you cheat you are more likely to do it and when a person cheat they may tell their partner they wont do it thats a lie because have more than one person in you life keeps you busy of one is not avaible then you got o the next one

The abstinence violation effect comes into play:

http://www.psychology-lexicon.com/cms/glossary/glossary-a/abstinence-violation-effect.html

Basically, when a person cheats, s/he will suffer extreme guilt and make an internal attribution to explain his/her behavior. I.e. "I cheated because I am an intrinsically bad person and can't be faithful." Social condemnation intensifies the guilt, especially the oft-repeated quote, "Once a cheater, always a cheater." While it's true that some people cheat without remorse, many people feel guilty about cheating, but then they believe in the truth of that aphorism, and it becomes a self-fulfilling prophecy.

Also, as Duke pointed out, the factors that precipitated the cheating may still be present. For instance, if you are unsatisfied in your relationship with the person you cheated on, but you stay anyway, you are more likely to cheat again.