I think you have a while to go before you should give up and run. But that should be an option you aren't afraid of if you are certain you have exhausted all tries at resolution, with no success.
But let me suggest another way of looking at this. You have said that you don't have custody. It sounds like his mother and her family don't have a whole lot to say good about you, and nothing good to say about your wife. And it doesn't sound like that will change. Perhaps you should consider moving just you and your wife, accepting that your aren't going to have a good relationship with your son until he is older and able to make some of his own decisions with more independent facts.
I was in the 7th grade when my father died. For a very long time my mother didn't seem interested in dating again. I thought that was correct and proper. Honor to my dad and all. Then she started seeing a guy. I was very jealous of him, and hurt by my mom. How could she? Then for a reason she never fully explained, she broke up with him. I always suspected he wanted something she wasn't willing to give outside of marriage. Later, she met and started dating another man. He was a really wonderful man. But that didn't make any difference to me. I was jealous of him too, and so didn't like him. Hey, mom didn't need a man around the house, I was there. How foolish we can be sometimes.
Later I joined the US Army. Through basic and AIT, it began to dawn on me that my mother didn't have me any more. I wasn't there to 'protect' her. I started to feel bad. Then one evening I called her and she hesitatingly told me she had gotten married. I can't really tell you how relieved I was to hear that. That was when I began to look at my step dad very differently. He was a wonderful man in any way you would want to measure him. They were very much in love with each other, and I was so happy for that. And thankfully, told her so.
What I hope you can see is that kids can get some very crazy ideas, all on their on. Is your son jealous of your wife? Is he angry at you for 'abandoning' him, and hoping to get you out of the marriage so you and your ex can get back together? Who knows? Your son may not even really know. In my case, until I had my epiphany, nobody could have convinced me to be anything but antagonist against any man my mother dated.
You owe some things to your son, and moving away from him would not be easy, and might cause both you and your wife to feel guilty. But remember, you made some explicit and non-explicit commitments to your wife as well. Getting your son to change his outlook at this point in his life may be difficult to impossible. Something to consider, but I don't mean to tell you what to do. You are the only one in the end, who can really say what will be best for you. And whatever you choose is something you have to live with for the rest of your life. I hope you choose well.