My girlfriend spent the weekend with her ex, what do I do?

When we first met the ex boyfriend always lingered in the background, he constantly tried to contact her, she always told me how he mistreated her, and that she never wanted to see him again, It was a long weekend and I made special plans for us to spend together, when I tried to contact her that Friday to pick her up,her phone was off, I then called the house phone and her father answered,He told me that she's spending the whole weekend with her ex, I was completely destroyed inside, I really love this girl a lot, but I'm afraid I'm gonna lose her, I'm completely confused and have no idea what to think,or where to go from here,she is not answering any of my calls.
My girlfriend spent the weekend with her ex, what do I do?
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