I’ve just had a look and he’s taken out over £3000 in the last 4 months.
Some of that is Xmas presents for his family, but that’s ridiculous and not the way I want to live.
So that's averaging £750 PER MONTH ! On HIS 'hobby' ? (The whole of December's £750 got spent on presents for his family ? Well, he's very generous !) What did he get you for Christmas by the way ?
Where's your £750 per month to spend as you like ? Oh, that's right, there's not enough money in the bank is there ?
He's secretive about the spending and has pretty much hidden the items he buys. Why ? Because he knows you'll be cross.
Your relationship seems to have gone parent / child.
Him using joint bank account money AND savings to fund his hobby is pretty much theft. (Yes I know it's joint property but the secrecy of it seems like theft.) Does he not want a future with you ?
He veered off of the agreed amount to spend each month and got a couple of credit cards. Sounds like he's rebelling in a very juvenile way.
He resents only getting an agreed amount of spends from the joint account. Which is why he got a couple of credit cards so he could spend up as much as he wanted without you commenting. Then the cheeky bastard uses joint bank account and savings money to pay for things that are for his entertainment. He needs to grow up. Tell him this behaviour is undermining your trust in him. He's probably past caring tbh. Good luck.
Demand to see the items that he's purchased. How much did they cost ? How long is he planning on keeping them ?
Investment my arse. He will never sell them. It's a form of hoarding.