Why do we cheat in relationships?

i have cheat my lover.. it's seem like white lie. when you lie to your girl/boy, i know that there's a reason for their action. maybe her/his love try to hold their love so tight and didn't give much space to develop their self. i ever did it. i know i'm wrong but i have a reason for do that. he never give me room to develop my own self. he always wants me to be near him. i can't even have time or make a decision for my own sake. he's overprotective. i guess all that you need in relationship is thoughtfullness

I think it's because they feel they've been cheated in life so they do it themselves. Or maybe because they are not satisfied with their present relationship.