In that case then I would explain to him that you are telling him to be respectful to him as he is the father of your children and not requiring his permission.
It sounds like you have all contact sorted and his only concern should really be about if the person you are introducing to the children is a good person, not the fact your in a new relationship.
Although you may be mindful of how he might feel when he is told, as he is now regretful, it sounds like he’s caused a lot of upset and heartache. It’s your turn to be happy now.