Ex becoming very awkward since the arrival of his new baby with new partner

Tables have turned. You've got a new man and are jetting off to New Zealand. He's doing the baby stage all over again. He's being difficult because he resents that you are happy.

Use one of the court approved apps for all communication and contact arrangements going forward.

Ask for a "lives with order" in your favour. It will be interesting his response if you offer him increased contact. If he doesn't want it but then objects to you going in holiday how ridiculous will he look!

Anecdotally, outside of South Africa which has very specific policies around travelling with children, I have never been asked to prove that my husband approves. I HAVE however, regularly been asked a few questions just to check who I am/ who the children are/our relationship (probably in part as we don't have the same name) and weirdly, this happens in particular on my return to the UK even though we're all travelling on UK passports.

This is true for every other woman I know.

HOWEVER, technically, you need active permission from all adults with parental responsibility. Now, in my case, DH doesn't send that in writing (outside of SA, as mentioned and frankly, I would 100% check NZ as it wouldn't surprise me if they have something similar) but it is implied and, of course, any border control could contact him at any time to confirm that he is happy with me travelling with the DC. I do not know a single person who has had this happen to them, but it is theoretically a possibility.

The real problem is if he decides to proactively make it difficult. There are mechanisms for him to alert border control that you are taking the child out of the country without his permission. I don't know anyone this has happened to but I've heard of it.

It is a very common threat however by narcissist men who are struggling to find ways to continue to control their ex partner and their dc. If you think he's the type who might vindictively contact the authorities, you will absolutely need to get some kind of court order that as the resident parent, you can travel.

Are you in the UK? Do you have court agreed 'lives with' custody (I don't know the official term)?
My DD had a similar problem with her ex objecting to her taking their DC abroad for 2 weeks. Her solicitor advised that, as she has resident custody (or whatever), she could take DC on holiday without ex's permission.
Perhaps your ex thinks the guy you are seeing is going too. so playing happy families with his son.

Yes, definitely work on that. I wouldn't mention the holiday again until you have the relevant court documents. You know full well he will act all surprised. Don't fall for it. Keep up the momentum. Tell him anything court appointed protects you both.
You are dealing with a disgrace of a man who abandoned you at your most vulnerable. He is not a good person. I suspect he is regretting his life choices and taking it out on you. The most powerful thing you can do is ignore him.
You shouldn't have to do any of this but you must. He will dick you about and won't think twice about what is best for his child. I have a feeling that he will be reluctant to have any contact set in stone, he is just grasping at anything to use as a stick to beat you with.
You can do this. You can provide your child with the best home, with the best experiences, love and light. He can't do that. He knows this and it bothers him.

Stay calm. Why are we here? We used to coparent well but now we are disagreeing over holidays etc so I want to get things formalised. Why won't you agree to the holiday? He can spout xyz, you can say you've offered make up time, he didn't have him for longer when new baby born etc. He will look like the twat at mediation, and at very least he should consult a lawyer who will tell him courts will grant permission for holiday so he's just going to waste money opposing.

Wow. He doesn’t hang about does he? What a prince.

Just dont let him. During mediation stay factual, no emotion and if the poor me act starts, tell him he can sit shrouded in his victim complex when your not paying for it 😊 and just crack on. Ignore bad behaviour during the sessions and respond to good. Like you would a toddler.

Please let's not blame women for men's shitty behaviour. This woman is a new mother parenting with a childish arsehole - she has enough on her plate.

If he won't give a letter you need to get an order from the court

@quietnightmare "You don't need his permission to leave the county for a holiday. He has to get a court order to stop you"

You are mistaken.

If both parents have parental responsibility (eg they were married or the father's name is on the birth certificate), and there are no court orders in place, then neither parent can take the child out of the country without written permission from the other parent. The permission letter also needs to include the other parent’s contact details and details about the trip.

In contrast, as long as there are no court orders in place, you don't need permission to take your child on holiday in England or Wales.

I don't blame you. I'd want to murder him in your shoes.

First step in CAO is mediation so hopefully that will show him how much of a twat he's being!

Sorry, it is the new partner. You’ve filled a space that used to be his. How dare you! And you’ve continued with your plan to go to NZ, even though it can’t possibly be a good idea now he’s not going, can it? Ugh. Hope he stops being a dick

It will be the new partner. She'll be bitching about you going away to New Zealand and jealous so will want to put a spanner in the works by putting a flea in his ear about how he won't see his child for a month.

he flexibility in comtact - yes, this has suited me mainly but for a good 4 weeks or so surrounding the birth of his new child, there was a lot of leeway on my part ie he couldn't take DS around the time of the birth, (ex lives in another city around an hour and a half away, so I'm guessing if she went in to labour, it wouldn't have been easy to return DS so he could support the new partner) so he just didn't have our son for overnights for a few weeks. This impacted on me as I work shifts as a HCP, but I worked around it. So the flexibility hasn't only benefitted me.

Point this out. Remind hm that he didn't see his child for weeks when the baby was born, so why is this different? He can facetime and chat online with him and you're happy to let him have more time when he returns.

I'd say ask calmly again, ask what his issue is. If he's still being an arse tell him if he doesn't agree you'll be starting formal proceedings and he can either give you permission or have to justify his refusal in court, despite what you've offered in response. You don't necessarily need a CAO, but not a bad idea as prevents this happening again. There's also specific issues order. Hopefully the threat will be enough, he'd look a right nob in court.

Maybe as you and he had talked about your dream holiday to NZ,he now feels jealous of you going and him at home with his new baby?(Boo Hoo) He sounds rather immature to me . Is he quite young? Anyhow I would as PP above have said ,tell him he will have to have DS for 2 weeks I bet he will run a mile!