My ex-girlfriend told me that she was dating today.

First of all, did you dump her or did she dump you? I think he told you about her blind date because he was still attached to you and wanted to see what your heart would look like when you heard the news. This is not a blow to you at all. You think too much. If I want to hurt you, she will only say that I am getting married. I hope you can come to the ceremony.