The obvious answer is that they are unhappy with their partner. But, there are so many reasons that it’s really impossible to give a solid answer.
I think a lot of times people tend to forget why they fell in love in the first place. They become complacent in their relationship and begin neglecting each other. The fire that was there in the beginning will never stay lit unless both partners are willing to make an effort to stoke the embers. Boredom has a way of making people look for the excitement they once had. Sadly, the opportunity is almost always there and people do make the choice to stray in order to find what they think they lost.
The consumer mentality. People upgrade their phones, iPods, TV's, computers, wardrobe, cars, hair, house, music and movie tastes, and everything else. The idea of choosing a partner for life is daunting to many, especially if they live by the "latest and greatest" mentality. It takes a commitment on both parts in order to stay together. If either one begins "window shopping" then it's only a matter of time before problems will arise.
Bosh, do you visit msn.com or is it just a coincidence that they have a 'why do we cheat?' featured video article today, haha?
Anyway, I only watched a quarter of the video (it was an hour long) and this is what I got from it (bear in mind they'd only got round to discussing men by the time I had to stop watching, not women.. and only biological theory)>>
Men are torn between two evolutionary drives - should they stay with their partner and help nurture their offspring, or should they 'spread their seed' as widely as possible. Historically, the cheating man benefits, but there's a huge upside to sticking with a lifelong mate too, in that they essentially have her entire resources and investment interests in his offspring. So, males have a duel mating strategy. Their ideal is to have one 'long-term' partner and then 'short-term' partners too. This is a very high risk situation though, as polygamy is frowned upon by most societies.. so conclusively that's where cheating comes from but also why not all men cheat.
I think it's curiosity and this endless searching for new people to spice up your life.
In some cases, while cheating, your current partner becomes a second alternative which means after you find someone new in your life and you see it doesn't work out between you two then you get back to your previous alternative - your current partner. That's why there is cheating because you can't/don't want to break up completely/immediately from your SO.
So you save the partner for yourself until you can be sure about your new relationship... then you might break up.
Unless a relationship is forced, I think this is the reason why there is cheating and no break up, in the first place.
I may be wrong. Correct me.
I haven't cheated yet.
I would think there was/is something wrong in the relationship that wasn't making the one party member happy or fufulled with their current relationship standing. Like a controlling partner, children that weren't planned/expected any time soon, etc.
I would think some like to do it for the thrill, get the action done and over with then return to their homes and know they just did something and got away with it. But eventually with that mentality, someone is bound to make a mistake.
There must be millions of reasons but the main ones I'm aware of are: Bordem and insecurity. Bordem pretty much speaks for itself but I think a lot of people cheat because they feel insecure about themselves and their relationship. Maybe they worry that their partner is cheating or doesn't love them anymore. Maybe the love they get from their partner isn't enough for their self esteem. I do believe a lot of it comes down to ego.
Those are great ideas to why people would cheat on their partner and like everyone pretty much mentioned there's thousands of different reasons to why someone would cheat. But do you think that the #1 reason would be the lack of activity going on in the bedroom?? Meaning the person who cheats wants more action but his real partner wont give it to him/her.