Few things hurt more than being rejected by someone we once loved, and when they refuse to have anything further to do with us, the hurt is even greater. This is what you are experiencing -- and you're right: Your ex-husband has shown by his actions that he's concerned only about himself.
But God understands your heartache, and my prayer is that you will turn to Him and seek strength to leave your anger and hurt behind. Your ex-husband probably isn't going to change -- but will you? God understands your anger -- but what will your anger do to you and your children if you don't overcome it? The Bible says, "Anger is cruel and fury overwhelming" (Proverbs 27:4). Anger and bitterness can be like poisons, hurting those around you and eating away at your soul.
How can you overcome this? First, accept the fact that you can't change the past. Then commit your life -- and your family -- to Jesus Christ. He not only forgives the past, but He also wants to guide you in the future. God loves you, and the greatest discovery you can make is that He is with you in the midst of your heartache.
Then ask God to help you saturate your home with love -- love for your children, and most of all, love for Christ. It will be the greatest gift you can give them.