@Mumshine101
I get the feeling they are going to move in together and this is why this is happening now, I’m just not okay with that. I think my kids should have their dad to themselves for a bit longer than introducing someone new
I'm afraid that although it's feeling very hard for you, this is something you're going to have to get used to.
He wants a full life with a partner. She's been with him a year. Nothing has been rushed. If he's waited this long to let the kids even meet her then he's been very sensible.
He's also, IMO, probably tried to give you time to get your head together.
This is a critical junction now for you and your children. How you react now will affect your kids more seriously than you can imagine.
What you need to do for your kids now is NOT to fight with him or resist this.
You need to fight YOUR instincts of jealousy. You are a mother defending the father snd kids against another 'mother'. You cannot let yourself do this.
Cooperation and respect between you and him is an amazing gift that you have the power now to give to your kids.
My very strong advice to you would be:
Change your tune with him right now.
Say you're sorry, you know this had to come and of course you are ok with it.
Say you appreciate him having waited so long.
Say you think it's best for the kids if he could make sure he's always positive about you to the kids, and that she is.
Say you'll do the same and be positive about them.
And then don't make any big deal AT ALL about it with the kids.
'Oh did you meet (x)? That's nice.'
Nothing more. Bite your tongue.
You could be helped by some private counselling for your own feelings.
I'm afraid these are the new challenges you'll face in jot being together with him. But in time maybe you'll have a new partner. And you'll want him to be in your life. You are entitled to that, as is your ex.
Flip it: how would you feel if you met a guy and didn't let him meet the kids for a year and then your ex said he'd take you to court if you dared let the kids meet your boyfriend?
It's not reasonable. You MUST behave differently.
Or don't, but it will lead to years of misery for you, and especially for your little ones. They need the adults around them to get on.