B1
If something bad that has happened is someone's fault, they are responsible for it.
Dictionary examples:
Is it my fault that your plant died? I watered it with soda! (0.0)
It's the alarm clock's fault I slept through three meetings! (0.0)
It's not my fault the dog ate your homework and your shoes! (0.0)
It's not my fault she didn't come! (18.6)
She believes it was the doctor's fault that Peter died. (24.2)