My SIL lost custody of her kids to her ex-H following her own worn out feelings and leaving the kids with her ex-H so she could have a break and her ex-H then filed for full custody and had the better lawyer and won. She has them back now, but I don't think she will ever forgive herself for the 2 years the kids were with him.
If you and your ex-H stop dating, would that really kill the friendship and co-parenting relationship you are slowly building up? Would there be legal grounds no for you to propose altering the custody and access arrangements?
I think you are doing fabulously and I don't doubt that you will have a new fulfilling and wonderful relationship with your ex-H. Even though you are not with your kids, you can still express your feelings of love to them (which is why I suggested the journal - I have one for each of my kids). You will need to be patient with your ex-H as he will continue to test and see if the new you is permanent. He sounds like an over-protective parent who has to learn a new reality.
Current Thread Me: 39, H: 35 Kids: S14/D13/D11 1995-04 Married 2003-08 Bomb 2003-09 Separated