Coming at this from another angle.
I think the parents could have a lot to do with this.
I think when it was just the 2 of you discussing this I got the impression he thought it was a great idea.
Unfortunately he discussed this with his parents and even though he is nearly 40 I think they see their little boy having the big white wedding and him walking back up the aisle with a young woman who doesn’t have a ready made family
In their eyes whilst he was going out with you/living with you he was just treading water. It didn’t matter
Buying with you I think has set off some major manipulation on their part as their dream was going to be shattered.
They had to break you up and unfortunately I think they wound him up so anything you said would have been seen as a reason to call everything off.
FWIW I think in time he will regret his decision.
At nearly 40 I know he isn’t up against any biological clock but the older he gets the older the women he dates will be and to find a woman who is nearish his age without children is going to get more and more difficult
I don’t actually think if you got to the bottom of this it was about money
This rang so many bells with me as I know someone who was akin to the son in this (he was in his 40s) and his parents did so much work dripping negativity on his choice of gf and on getting him to split with her because she had been married and had children. (Gold digger/you won’t know if any children she has will be yours type rhetoric)
They had in their minds eye the picture of the girl he would marry.
He is in his 70s now and lives a very solitary life. Never married, never went out with anyone ever again.
The reasons he has given and got enraged at are really petty
He said he didn’t want to have children with someone who he wasn’t living with.
But then leaves you pregnant.
That doesn’t even make sense