Single Parenting Support Group
Today being raised by a single parent is not uncommon. About three in ten children live in a single parent home. The most common type of single parent home is one with only a mother. However, single father homes are the fastest growing type of family situation; 60% growth in the last ten years alone.
Maybe he will change and will cherish that relationship but now is you and your son. Your ex walked out of your life. Take it from someone who is struggling with "coparenting" with a person that wants to be in my child's life but doesn't give a damn about the how, that does not give a damn about me as a mother and takes my child to play happy family with current girlfriend. Unfortunately, I do not have any more words of advise for you other than enjoy what you have, it could be worst.
Take all the measures to protect yourself, document everything!!!!, it may help you in the long run. Also, there are organizations that help with domestic violence, they have programs that can assign people to go with you to court. All the best!