The ultimate consideration is what is in the best interests of the child. How old is your child? Is he old enough to have an opinion about staying with your current partner? If he is, that should be taken into account. If he feels safe and looked after staying with your current partner while you're away, then you should make your wife aware of this in light of the ultimate consideration that the Family Law Courts consider - the best interests of the child. (Or if the opposite is true, then you need to consider whether him staying with your ex while you're away is in his best interests.)
Given that you started preparing Consent Orders 18 months ago, I imagine you’re aware that a parenting plan is not a legally enforceable agreement (unlike Consent Orders or a parenting order where you can go to the Family Court for a penalty if the other party breaches the terms).
It might be worth re-writing your parenting agreement to take into account your children being looked after and spending time with your new partner. You might want to apply for that agreement to then be made into Consent Orders with the Family Court. Or apply for Parenting Order if you can’t agree with your ex - there is mandatory family dispute resolution which may held sort things out. See
CathL’s LawAnswers Family Law Forum Post in relation to outlining parenting arrangements that are legally enforceable.
