This is a great time to read, read, read, read. Great books are Not Just Friends, The Five Love Languages, The Language of Letting Go, Unconditional Forgiveness, He Said She Said, etc. Read and absorb it. Talk about it with your friends, here and around you.
I worked on me. Even though it seemed unfair. He was the meanie who left! The injustice! I felt the soul shredding embarrassment of being a cliche... clueless, traded in. It took time, lots of time and practice, learning. That's where having a good counselor comes in very handy. They are experts in helping folks work through the spaghetti of emotional conflict. If you broke a bone, would you set it yourself or see a professional... just saying.
When talking to my husband was hurtful and counterproductive, then it was on the phone. When that turned out to be horrendous, then it was email. That was when the 48 hour rule came in very handy. It's funny, even 3 years after the divorce, his manipulative antics can still get my heart rate up, my anxiety in full swing. Now I know to sit back, take a deep breath and walk away. I address him on my terms, calm and in control.
In divorce there's two types of parents. The ones who leave the spouse but want the family/kids and the ones who leave them all. Mine left to a 'complete' life with her. At first I was in agony over his treatment to our kids, seeing them twice a month for a one hour dinner. Now it's down to 4 to 6 times a year. They had to fight to meet their new brother which occurred when the baby was 11 months old.
One of the worst things I did was always breaking down when the kids and I were together during something significant.. like one of their birthdays or holidays and cry, apologizing for what was lost with the divorce, that inherent vow I made when they were born. Eventually I realized I was the one having the problem, not them. Talk about learning how to drain the pity party pronto!