Yes, it does usually take two people to end a relationship but the person who ultimately wants out will often exaggerate the problems, the 'faults' of the other person to make themselves feel right in their decision. By doing this, the already devastated other person will feel even more responsible for what has happened. They will feel if they had been better, if they're done more things right, if they'd just met their needs all would be fine. It leaves you in a crushed state constantly wondering what it is you could have done to make it better.

Let me tell you, there's nothing you could have done. When o­ne person decides they want out it's not possible for another person to force them to stay no matter how much you love them.