Hi,
What appears from your text is that the girl you were dating on and off has stopped talking to you suddenly. This phenomenon is known as ghosting and has become quite common - people disappear without a reason or explanation. In such cases you are left wondering , what have you done wrong.
Next Steps
Do seek therapy to work out whatever this person's ghosting is making you feel and move forward in life.
Health Tips
Chasing the other person may not help. Instead you can focus on your own self.