How do I cope with this!?

I don't think from the posts I have seen on MN, that it's unusual for a man, to move on very quickly after a divorce/separation. Whereas, I think women tend to be a little more cautious, and that may be more to do with the fact we are normally the primary carers. I think it's hard on your children, that your ex has moved on after 4 months. However, as you're separated, and it was your decision to end the relationship, you can't say too much. Ultimately, it's none of your business. Yes, it may have been nice for him to have told you, but he didn't and doesn't actually have to.

Been in a very similar situation and of course you're allowed to be cross and hurt. Mine was playing happy families with the in-laws six weeks into a new relationship six weeks after I'd told him I was leaving. Bang went any illusion that the two decades I'd spent as part of the family meant anything. I was very easily replaceable it transpired.

But this is what a lot of men do- heal themselves by just moving on and not dealing with any of the actual issues. Tale as old as time.

The respectful and grown up thing would've been to have told you first, but it also takes guts to have that conversation and he's obviously not up for the trickiness of that.

I'm really sorry he's behaved like this, but at the end of the day as long as your kids are ok anything is bearable. But it is still hurtful and your feelings, whatever they are, are valid.

That’s the spirit! That four months will have flown by for you, but will feel so much longer to the DC.

I have been a child who had a step mother, been a step mother myself, and now my own DC have a stepmother, so I have experienced various angles.

Your priority has to be are the kids OK? They probably aren’t remotely interested in daddy’s new friend at this point, but if they see you kicking off about it they may become unsettled.

This is what you NEED to focus on.

The kids didn't ask for you two to get married.
The kids didn't ask to be born.
The kids didn't ask for you to tell their dad to leave.

If the kids seemed to really enjoy it, you should be happy for them!

They've been through a hell of a lot, so any happiness they can grab (especially the first Christmas with separated parents) should be welcomed.

I'm not saying it's easy btw, but you need to shift your focus off your own feelings.

Why did you leave him?

He clearly lacks emotional intelligence.

I have dated fairly prolifically over the years and many, many men will happily bumble along from one relationship to another, trailing their unprocessed emotional baggage with them.
Being on their own is more painful than each new relationship not working out.

You are really struggling to accept that he is doing things differently from you aren’t you? For your sake and DC sake, you need to come to terms with the fact that he doesn’t have to dance to your tune.

You decided to have a few random bunk ups but he decided to have a full relationship. You would discuss with him before introducing DC to new friends (so you say) but he hasn’t. If DC are young enough to visit Santa, they have probably just been introduced to daddy’s friend.

Do you consider yourself banned from making new friends and introducing them to DC? Of course you don’t because it’s batshit, especially four months down the line.

You can’t control this so stop trying, you will tie yourself in knots, make yourself ill and look foolish. Taking his DC to see Santa. Yeah, what a cunt 😂

I would be annoyed too if someone introduced a new woman to my dc so quickly after breaking up. Yes he is entitled to see someone new but it’s only been 4 months, the kids are probably all over the place without introducing someone new to the mix like this. It’s pretty selfish doing this.

What difference would telling you have made?

Clearly he wanted to do something together with them, and her. Santa sounds nice.

Did she have children involved in the day out, too?

What did your kids think about the day? Have you had any feedback from them?

What? You left him, he hasn’t cheated, is allowed to do what he wants, isn’t with you and you feel you can lose it on him for making a reasonable decision.

Why was it a shock? You aren’t in his life anymore to know the ins and outs. Did you expect him to stay single until it suited you?

For the sake of the children I would suggest you consider your reactions to him when he has done nothing wrong in future.

This is a good point. At least he seems to be taking it relatively seriously with one woman and also looking after his kids, while the OP is off having random sex with different men.

I don’t know why you’re hurt about him being in another relationship when you’ve had rebounds yourself in the 4 months. You both seem happy it’s ended as you’ve both moved on technically.

Him being in a new relationship is just the same as what you’re doing, even better because at least he’s with someone rather than having rebounds with randoms.

The issue here is that he’s introduced the kids to her which is too soon and not putting them first. How to help the kids navigate this should be your focus.

It was very selfish for him to take the kids to see Santa with her. That is usually a really special family activity. So yes he was 100% in the wrong and also in general it’s not fair on the kids to be introducing another woman in a “mummy” figure who he barely knows himself.

However OP…. four months really is nothing and it sounds like you’ve both rebounded pretty speedily in your own way. Perhaps you could both do with prioritising the kids for a while and taking time to discuss how you are going to navigate this massive change for them rather than seeking relationships and/or hookups.

Why does it hurt you? You dumped him four months ago. You have no say in his love life or in what he does with DC so long as they are safe and cared for.

Did you think he would see the error of his ways and come crawling back, a changed man?

All you can do is hope he has chosen a lovely new partner who will be kind to your DC.

You don't want him. You gave him freedom and he has grabbed it with both hands. Welcome to being divorced with kids.

He’s a pretty selfish prick of a father for playing happy families with his new woman and kids already. They’ve not even had time to adjust to your separation yet and he’s already bringing step mum number one into their lives.

There really isn’t anything you can do to stop him prioritising his dick over his kids wellbeing but just don’t bite and give him any reaction.

Ok but you didn't address what I said, after quoting me?

Remember all his flaws. Well someone else gets to deal with them now.. Maybe not immediately but they will surface. And nowt like dampening a new relationship than 2 dc... He's using them to play Good Guy. It won't last will it?