I really feel for you, I do. It all sounds so familiar, about "never", that he won't be in your life, that he wants to be with the OW. SO when I say this, it's not because I didn't taste my own medicine but because this is the medicine that helps me in a similar situation:
try to recal how many times in your life a situation was looking hopeless and devastating, and yet somehow things turned out for the better? How many times did you say to yourself that you woudn't have luck in something if not for some bad luck before? How many times you lost something and then unexpectedly gained something else that was given to you out of thin air?
Then, try to think of yourself as a person who posess the ability to turn a bad situation to your advantage through say, serendipity. Hold that image of yourself and see what happens.
To get through the darkest period of the night, act as if it is already morning.
The Talmud
