Broken hearts

It is amazing to me that my heart can feel so broken right now. I was in a bad relationship, I finally ended it and I felt GOOD. But then my ex moved on to a new girl.  It was only 3 weeks and he was calling someone else "his love".  I know we don't belong together (I have a list of reasons) and that I don't want to get back together with him, but it still hurts to know after 4 1/2 years that I can be replaced in 3 weeks. He was my best friend for over 4 years and I don't want to see him hurt again. To make matters worse, I think the person he "loves" is a relationship addict.  Her social media sites show multiple people she has "loved" in the past 9 monthes.  I know I sound cynical, but I went out of my way to end things well with this man and I do not want to see some woman who loves any man who pays her attention break his heart again.  ...sigh......