New York and Mass. are bordering states, so you may be close or you may be far apart. How far away is he moving from you? Will he be close enough for 50-50 to work?
I think you probably have some legitimate complaints, but you seem a bit too hard on him.
You demean him for moving in with his parents, but you did the same thing.
You complain that he doesn't pay you enough money, but he is working two jobs and you are not bothering to contribute anything financially to your child.
Instead of complaining that he only works a second job because he "wants" to (Yeah, right, he probably HATES having free time to relax.), stop making excuses, get a job and start helping out.
You say you are willing to let him be with his son any time he wants, but you aren't willing to give him 50-50.
You complain that he is "choosing" his girlfriend over his son, but YOU walked out on him, so he has every right to move on with his life. Most parents have a spouse or SO in their lives and it is not a matter of choosing one over the other. He can love both his son and his girlfriend. Besides, he says he wants to bring the child with him, not choose one over the other.
This leads me to the only thing I agree with you on, but it is the most important thing: The father is making a huge mistake moving away, whether he takes the boy with him or not. Either way it makes the life of the child a lot worse.
To answer your question: Do you have a chance at custody? Yes. I just wish sometimes people would stop asking that question and ask what would be best for their child.