I think some people are under the impression that you are banned from co-parenting when you have split up.
Of course you are able to have reasonable input into the other parent's parenting, reasonable input and to prevent your child being unnecessarily harmed or neglected.
What you aren't allowed to do is alienate your child from the other parent. This guy is doing a good job of alienating his own child.
The op mentioned that he doesn't have plans to do anything with DS because someone else said she was unreasonable asking him to cancel activities he was doing with DS to support activities she was doing.
Her point is, there is no reason at all for him to not support DS' activities on these weekends - he simply won't do it because he wants his son there and he won't have her changing things.
He promised the judge he would support DS' activities it can be written into a court order that that forms part of contact. I think some people are forgetting that contact is meant to be in the interests of the child not for the benefit of the parent.
And I will just leave this here; this man thought it was, and has been supported by SS, CAFCASS and the court to think it is, OK to punch him in the stomach so of course the op is worried about his competence and care - in some ways the services have left them to fend for themselves.