Modification to a Rule 11 Custody Agreement?

My 16 yr old daughter went to live with her father just over a year ago and we signed a Rule 11 Agreement to change primary residence to his home, for him to stop paying child support to me, for me to now pay a fixed travel allowance provided my ex paid the full travel costs since he was the one who decided to move 5 hours away from my daughter. It's been a year now and he is asking for a change of venue to his county, for me to pay her travel expenses and to also pay child support. He is stating that the circumstances have materially and substantially changed since the Rule 11 Agreement was signed. But nothing has changed. Unless he means, he got married and had a kid? I have three young kids in my marriage now and also work, so I am concerned about the financial impact to my family as well as the possibility of having to travel to his county for several hearings. What is the validity to this? I feel like a bait and switch has happened where he said agree to this.