Partner maybe having mental break down ?

Affair.

Whatever the reason for his behaviour, it means he has to move back to his house (even if it’s temporarily) so you can protect yourself and your kids from his abuse. The kids will know when you’re upset, you can only shield them so much and that’s not fair.

Leave.
In this scenario you dont do everything for joint child it sounds like he never has chance to be a dad anyway. If you did and do everything and he just mows lawns!
But is beyond that now
He might be unwell but if he wont see gp you need to get out and away

Please, please, please @strugglingtbh tell him not to come back to your house. He is abusing you. He might be ill but it's not your fault and it definitely doesn't give him a pass to be abusive.

Please try to find your anger, how dare he speak to you like this and blame you for his inadequacies. Tell him he doesn't not get to speak to you that way, that you and the kids don't feel safe so he should go back to his. If you want you can say you love him (I wouldn't) and he needs to get help then he can speak to you. Expect the abuse to ramp up and please tell people around you and call the police if need be.

He needs to leave and luckily, he has somewhere to go. So off he goes.

He’s not having a mental breakdown. He’s a jerk and is abusing substances. I didn’t even get to the cannabis bit, but I could tell this was going to be a drug and/or alcohol problem. I would bet he’s drinking too. But yes, could also be caused entirely by the cannabis. He needs to quit and sort his behaviour out or he needs to go. This is no life for your children with an explosive addict.

You don’t have to put up with this shit. If he is having a breakdown he needs to seek help and stop smoking weed. Not drag you down with it.

His behaviour is abusive. It’s negatively affecting you and your child. Leave and stop making excuses.

OP you're doing the classic woman thing of trying to work out why this is happening, trying to improve things by getting him to go to the doctors, asking questions, trying to cheer him up etc. Rather than realising it's not your problem to solve, and that your responsibility is towards your kids and yourself, to protect yourselves from abusive behaviour. It's for him and his medical team / therapists to figure out why and put steps in place to help. You do need to protect yourself and your kids as a priority, he sounds extremely angry and it sounds like the weed is causing him to spiral, please get him to leave

Tell him not to come back. Be ready to call the police if he turns up.

Call Women's Aid, your local domestic abuse organisation (Google it), or The National Domestic Abuse Helpline for advice on how to stay safe and some support.

How long have you been together?
How old are you?
Did he really want to start a family with you at 47yrs old?
Did you pressure him into it?
What is the financial setup of your relationship?

None of the above excuses his shit behaviour but it might give a clue as to where his anger and issues are coming from. I am not much older than him and i would rather stick needles in my eyes than start with young children again.

He may be on the verge of a breakdown. Or he may be a twat. Either way, you are the parent of 3 kids (including a 2 year old) and you need to put them first.

His behaviour towards you isn't acceptable. Can you get some counselling together to establish that boundary? That you understand he isn't happy and want to support him but he can't take his unhappiness out on you. If he does then you have no choice but to separate for your and the kids' sake.
You can continue to try and encourage and support him to get the help he needs. But you can't "fix" him if he isn't willing or able to take steps himself and if he's taking his unhappiness or illness out on you.

Whatever's going on with him is aimed at you forcing the issue and chucking him out so that he can play the victim.

You've told him he doesn't have to stay but that still makes the decision his which isn't what he wants.

I’d also say he is having an affair.

Regardless he is not a good man. Escape if you can.

What’s your relationship like with dad of older kids? If he’s still involved and decent he might be someone to help you with the practicalities of getting current partner out of the house and police / MH services informed. He certainly should care about making sure his kids and their mum aren’t exposed to this. But obviously if he was also an asshole that’s not going to work. I’m so sorry you’re going through this. First priority has to be protecting yourself and children, then you can look at finding him help, if he will accept it.

Whatever is wrong with him, it is never acceptable for him to abuse you.
The fact he might hate his life is in no way your fault, whatever he tells you.

Has he even spoken to a GP about his mental health? There are no quick fixes but he has got to seek help independently.
Taking out everything on you is not a solution.

While he is at work, start seeking advice on your entitlements if you leave him.

OP you need to get away from this man before he drags you down with him. You own your home, you are a competent mum, you have your life together. You can go back to work and support yourself. You don't need to live with an abusive drug addict who says terrible things to you and ruins your life, and you don't need your son to grow up with that as his roadmap for how his mum, and women generally, should be treated.

Tell him he has to move out of your house. Keep in touch about your child only. You and your children deserve so much better than this.

Maybe the other woman has dumped him so he’s acting out.

Surely your life will be easier without him? He has no good points as far as I can tell. He is abusive and he doesn't give a shit about his own child. He is making you anxious and upset.

If your house is in your name and you aren't married, you can change the locks. Can you go back to work earlier than next year? Speak to Citizens Advice to see what financial help you can apply for until you are able to return to work.

What job does he do? Is there something going on at work? It sounds like he is deliberately trying to push you away.

Nothing to suggest he’s having a mental breakdown though, he just seems like a common garden variety prick who is never happy with what he has and so, always has to make that his partners fault somehow.

Look at those abusive messages. Imagine your daughter showed you that screen and asked you what to do. You would say kick him out. No one deserves to be spoken to like that. Now, follow your own advice.
Perhaps he is having mental health problems, perhaps it is cannabis addiction speaking, perhaps both, perhaps he has always had a nasty streak and it is only now surfacing. But no one should be spoken to this way.

The weed will tip him over the edge. If he isn’t having a mental breakdown, he soon will be. People underestimate that drug. It isn’t harmless at all.

So tell him to fuck off and he can be free of you. This is horrendous. You have a child to protect, stop being a punchbag for his outbursts.

I’ll tell you what you do, you choose yourself for once in your life.

Why on earth are you bending over backwards for someone who calls you horrible names? That’s not a partner it’s a bully. He doesn’t give a crap about you and heads up, he’s probably having an affair cause that’s usually when they start treating you like shit if it’s out of the blue.

Here he is treating you like absolute garbage and you’re still going “how do I make his life easier?”. Fuck that shit op!

Find your anger.
Find your self love and resepct.

He is a loser. Any man who treats his partner the way he does you is a loser. Get rid of him and value yourself. Teach your children we don’t stay with miserable bullies.