Didn't you just answer your own question? He is 4, he has supervised contact only order, dad left his child at 5 months, he only started seeing him Feb 2024. A child has only just got to know this stranger over 18 months.
How do I know this GF is a long term relationship, how can I provide that assurance. My child technically just got a dad and now this woman has come without me, the primary carer knowing. I don't know if she is abusive, if she has played a part in keeping his dad away or if anything for that matter. She could be vulnerable. My child is 4.
Don't you think a child's wellbeing is paramount and safeguards needs to be in place during the time the child builds a solid foundation with an absent parent?
If his dad was thinking of his wellbeing and understood him and really evaluated where this child is at emotionally and psychologically only after 18 contact sessions with him, then he would have chosen to plan, speak to me, understand if this is safe, let me speak to his girlfriend, let me assess and speak to his dad to decide if this is the right time. Or get a variation of the court order since it's supervised contact only.
He could have asked if he is getting a new mum, because in his head he only just got a dad after most of his life, dad wasnt interested before. Now, his dad has shown him a family unit, that he hasn't had. He has a brain of a 4 year old. He isn't a teenager or adult yet.
That's a child focused perspective. Not sure yours is. But thanks for your opinion.