She could have left home at 16 if she wanted to!
What a weird thing to say. And even if she did, she's not emigrating alone at 16, is she.
That's not even the issue here.
Correct
Me moving abroad with a joint child who wanted to move for her own future?
Well, that covers you and her.
She might not have liked it and moved to her dads.
Please. You're suggesting that if she hadn't liked it, you'd have happily stayed in a different country alone and watched your only child move back to the UK to her dad's?
Her dad has another child he's more invested in, dd can see that she's not stupid.
Well, naturally it would look that way, because he's in a family unit, daily with that child. That's down to you and him, not "another child."
You speak badly about him to DD. You agree she should be upset if his (and his family's) holiday is somewhere other than round the corner from you in the country you chose.
Was his wife to be, the other woman? I know you say you are on the fence, but you're so far from neutral on this.