I was the cause of my girlfriend's break up with her ex.
Does your girlfriend know that you were involved in her break up?
No, I'm afraid of how she will react if I tell her.
It's bad that you didn't respect their relationship when they were together. In the future don't interfere in people's relationships.
I can't believe you are judging me. Who are you?
It's not okay to break someone up so you can date them. You'll have to decide if your girlfriend will be more mad if you do tell her of if you don't tell her. Either way, you might lose her.