why do couples cheat on each other

The biological need, the desire and the pleasure people get while carrying on affairs secretly. This is very common where the society experiences too much freedom. In India it is quite rare to find such cheating couple.

I think the reason is that people find once they are married they no longer have to try to make the relationship work. Marriage is like everything else, if you want it to succeed you have to do a good job at it. We wouldn't get very far in our jobs if we were always slacking off and I believe relationships work the same way. We have to keep the lines of communication open and we still have to do all the little things which in the end are so important.

I do not know why, I do not think you should get married if you think you may cheat.