Why is this happening now?

It's your ex's fault for being such a useless parent and husband. Please don't be hard on yourself. I know it's really difficult but you didn't cause this.

You didn’t force your ex to go out all the time, to put his pleasure before his family. Your son is feeling insecure because of the changes, that’s to be expected, just give him lots of cuddles and reassurance that your not going anywhere.

One night per week? That's babysitting not parenting. Anyone could be dad of the year in such a limited time slot when they've got 6 days a week of freedom.

I do tend to agree with not messaging him.

The usual advice on the relationship board is to set up an email address that's just for his messages and block him on everything else. Let him know that if he wants to message you about the DC he should use that email address.

And there was a great thread recently where the OP was advised by her Therapist to use a very noncommittal phrase in situations like the one where he's telling you he has met someone else. She was advised to say things like OK or "let me know how that works out" although in your case I'd probably just go with the OK.

If he's not getting a reaction back from you he's unlikely to keep trying

Why on earth would you do that?

People who are sure they have done the right thing don't feel the need to send goady messages. Disengage.

Your son is feeling anxious because of the changes, your the parent who is always there for him as your ex was always out so give him lots of hugs, reassure him your not going anywhere.
I know you’re sad and angry but you saw you were a single parent even when you were with ex. You did the right thing by ending the relationship, he’s not going to see the light and become a different person because he is who he is. Don’t try to score points with him trying to make him see you were right, it’s just going to make you pissed off as he will use your emotions to play mind games.

Breaking up with him might be the best thing you've done for their relationship together to be honest. It forces him to actually parent them (even if it's fairly light and disney).
I'd give him some responsibility- here are their spellings, they need to do part of their homework, they also need 20 mins reading or whatever. If you do all the drudge you will be naggy drudge parent and he's all fun and games.

I'm on your side in this and he's a total shit but that text was unnecessary. It sounds like you're both goading the other.

Keep the contact between you polite but businesslike.

You are well rid of him @Beingamumistough he just thought of himself, going out all the time, pleasing himself and not bothering about you or Dc. He has them one night per week and actually has to look after them himself, it must be a big shock for him and he probably misses the time he could leave everything to you and go out all the time. Don’t fall for his mind games and suddenly being father of the year for one night out of seven. It won’t last long, he just wants you to think he has suddenly changed but it’s just an act. That leopard won’t change his spots!

My son was the same after I split up with his dad. He saw him regularly and I thought 'brilliant, I've done the right thing'. Then the contact started reducing and he completely cut ties 3 years later. Unfortunately that just confirmed it.

When it comes to the children just grit your teeth and see it out. One day the children will see the truth.

Mine are young adults/older teens and they know who did what for them (youngest was just two when he had his affair) and I get a lot of appreciation back these days even though I had to put up with the disney dad stage for a few years.

I never blocked contact but now he has moved area and rarely makes the effort to see them regularly. He wonders why they don't bother to see him (three can drive) but he reduced contact first and they don't see why they should make the effort he wasn't willing to when they were younger.

Honestly I'm with you, sick of 'em

I'm doing it on my own and it really isn't so bad. That said, it's always been just me

You can do this and you can manage the fallout from his, what i suspect will become, sporadic contact - routine, love, cuddles and routine, you've got it

How often does he have them? I'm guessing it's not 50/50. It's easy to be a "good" parent if you're only having them EOW (see Disney dad).

Everyone has said what i think tbh - stay strong girl, you've done the right thing

You've been brave and made the tough decision. It's a bit rocky now but will settle down. Let's see how involved your ex is after it's sunk in that you're not going back to him x

100% agree here

My eldest balled the house down as a 3 year old the night my dad was buried. He didn't understand the significance of the day, he was overwhelmed by the change to his routine.

Your son is overwhelmed, it will all go back to normal next week.

He is a master manipulator. Better that he does it outside your home rather than inside it. Your children will get used to the separate houses in time. I would lean into the positives as much as you can, which I think you're doing already.

He sounds like a colossal turd, your x by the way. Colossal!

I'm sure your little one was absolutely exhausted and that contributed to the tears, but it can be confusing and upsetting for children to understand why their parents aren't together. In their world, it's simple and, if they love both parents, of course they'll miss one when they're not with the other. Your DS can't know how unreliable and untrustworthy his father was, and not should he, but it's still painful for you to watch him dealing with that.
Be e strong. You know you've made the right decision when you reflect on why you ended it, but it's OK to have a wobble when you see your child upset.