why i feel so heart broken?

a woman i have known since high school that i dearly love has gotten married, she was never really faithfull and i went with her off and on through the years , i tried very hard to be in a relationship with her, but i allways felt like she was hiding something, we broke up a few years ago and she came back crying AGAIN saying how sorry she was, and wanted to get together and i sent her away,telling her that she would be tired of me in a few weeks and hurt my feelings again, now i find a few weeks after that she married . it has really damaged my ego and heart, i am 55 and had many relationship but my heart wants her even though my mind tells me, NO!, i know its probably for the best but i hate the thought of never seeing her again, it feels like such a loss, but really gets is is why i feel so desperatley in love with her, and NO other, at best i can put it away for a while, but it comes back, i know you cant allways be with the one you love , but BOY my heart sure doesnt seem to accept this well.