I believe that children can pick up on their parents feelings. If you are not happy w/this man I would have to think that your children sense this and overall they may not be in a happy environment. It's best for you to show your children what a healthy loving relationship is like versus settling for something to keep peace.
It seems like a huge disturbance if you were to choose to move out of state with your daughter being in high school - my advice would be to talk to your children and perhaps you could find another place to live w/in the area that would not up root them from their friends and school and even still leaving a chance for your son to continue on occassion seeing the man in your life that you wish to leave. Good luck with your decision!