Is it my fault that my parents are on the verge of separation?

Your parents have their own issues that they've been struggling with since before you were born, most likely. But that doesn't mean that you're the root cause of any of that or that you have anything to do with how they feel about each other. Some couples are forced into a relationship while others stay together well past a healthy separation point. Stress is a complex thing, try to be supportive of each parent.

Absolutely not! Whatever issues there might be, they are strictly between your parents. Even, for arguments sake, if they were having battles over how to discipline you, you would not be responsible. They are at odds with each other. I'm sorry that you are asking this question, at all.