His ex didn't leave that quickly, she cleared out his furniture and took his car.*
Something doesn't add up here. Most ppl wouldn't tale a car that belonged to a partner, knowing it was registered in the owners name as the registered keeper and that the owner could easily call the police and report it as stolen.
It's more like he bought her the car, because what would she think she'd get away with it.
You're choosing to believe everything he tells you and it just doesn't make sense... but you're so close and in love, you can't see it.
We've discussed what would happen if we split and I would be happy for him to continue to see my children
I think this is incredibly naive, given you don't know what the reason for the split might be. What if he was mistreating your DC or you? Would you still let him continue to see them?
Then if you have another relationship and split, the next Ex could want to keep seeing your kids. Where do you draw the line.
Alarm bells are ringing and tree flags are waving.
How old is he?
Why was he okay with his ex excluding the bio father? He stood by and accepted this...which was supporting her behaviour...denying the children a relationship with their father. Doesn't this concern you about him?
If he had an Ex that he refused to see their DC, for no reason other than spite, would you be okay with that?
This has all kinds of disaster over it. Your children are the ones I feel sorry for here.