That sounds like a really tough situation, and I'm sorry you've had to go through it. Everyone here is right, you need to move for your own sanity but also for your kids and husband. You gave that family time with your kids and tried to make it work, but it sounds like they don't appreciate it and they'd rather just use you.
You gave it more than a fair try, and tried to do the right thing by your kids and their dad's family, but it's not working for anyone except them. That is definitely not selfish.