I was with my ex for sixteen years had two kids.. thought everything was fine. I did everything, he wanted for nothing. Then one day he left and a month later was living with another women that he knew for some years. I can't make the pain go away, I hate that my children spend time with her. She is young of course.. I can't stand how his family has welcomed her into their family... The pain sucks, the anger sucks, I wish it would all just go away but it won't. I have found a great guy and I just want to be happy, but with the holidays coming it kills me that this other women is going to be sitting in what was my seat next to my children having Thanksgiving dinner. Will I ever be at peace or will I always be the women that was left

I had those same feelings the first time that my ex took our children to the beach. I wished it was me and couldn't stand that they were there pretending to be a family. MY FAMILY. Then I realized that as long as the children liked her and she treated them well, then any thing else was none of my business.
Be gratefull that you are not with a man who cares so little for you. Why would you want to be with him? Don't let his actions destroy you or your relationship with your children. The best thing you can do is to show him how great you've moved on. HE obviously isn't hurting over your lose. Make new beginnings for yourself and the pain will go away.