Why Lie?

Are you kidding me? I am seeing that alot of married people lie to their spouces about important stuff. Why lie? If you're unhappy or you can't be open with your spouce or you can't get along or you want someone else, say it. Leave. But why lie? In some cases why take vows in the first place when you know you're gonna be living a lie? How can you live with anotherr person, one you cared enough to marry and know you are a liar? The spouce on the other side of the lie always gets hurt worse. Not only because an event happened but then their trusted partner lies on top of it. I've seen money lies, I've seen girlfriend lies, I've seen addiction lies, but most of all i just see a liar-making excuses! Why lie?