I have two main thoughts...........if you still are interested.....
1. He is playing games with your childrens feelings....clean or using thats not acceptable and my thought is this may be good place to start with boundaries..........
2. he knows you he knows what hes doing and he most likely knows its hurting the kids and there for hurting you and if you play into his games you are just reinforsing his bad behavior your telling him,,,,,,,,,,,mess with my kids and I'll do what you want make them cry and I'll give you your way.....if you reward him for not signing the agreement by going around it or changing it somehow you were again manipulated