C.,
I have always been a single mom, my son is 18 almost 19 and my daughter is 10. It is not easy to be a single mom, but it does not mean your life is over. Yes your life should be about raising a healthy well adjusted child, but you too can have a life. Make time for yourself, you have too, it is the only way you will be able to maintain any kind of sanity. Now for the father, stop beating yourself up over him, he did what he did, and there isn't anything you can do about it. If he chose to get married to someone else, take that as a life lesson, he wasn't the man for you, however he gave you your wonderful son. And if he is willing to be a part of his life, then let that happen, if you are afraid that he will do something stupid, then seek supervised visitation and make sure you are recieving child support. And remember these words that my father told me when I had my son!!
If the father isn't going to be around, NO FATHER BEATS A BAD FATHER!!!
So decide if he really is a bad father and don't hate the new wife because she did not do anything too you, he did this, women always want to hate the women, yes women should be more respectful, but it was the man that left and you never know maybe she will be a great stepmom, having a stepmom does not mean your child will love you any less, you are the mom, never forget that and do not use your child to get to his father, that is not attractive or necessary, just live your life, love yourself and your son and good things will begin to happen to you and for you. find yourself a support group, be it your family or your friends or a church home, even a support group for single moms, but do things to better your life that way your son will grow up to be happy healthy and wise and know how to treat a woman. You are his mom, you decide what is best, but don't be bitter or angry because your son will pick up on that and you don't want that at all!!!
Goodluck C., you can do this, believe in yourself, love your son and start living your life, even though it hurts now, you will come out stronger in the end!!!