@Lilyandra Someone will probably come along soon, and say 'are you sure he's not depressed OP?'
He's not, he is just a miserable sod who can't be arsed with making a fuss of his WIFE on her birthday.
Also regarding THIS that you said...
"I'm confused tbh sometimes by his behaviour. He's not an enthusiastic person generally, so he is hard to predict. Normally after a few drinks he becomes happier and chatty. This isn't out of the ordinary to be honest, guess it's no different to any other day and it's my issue as I would love if he made a bit more effort to be chatty and interested on my birthday so maybe I just get upset about it more.>"
Red flags and alarm bells galore! He is only nice to you when he has had a few drinks? WTAF? 
If you haven't got kids with him, I would be thinking about whether I want to spend my life with this man to be honest. It's never going to get better, and you deserve better.
Just because HE doesn't care for birthdays, he should still make a fuss of YOU.
It's like the 'I don't buy greetings cards' brigade. They act like they're so wonderful and special and 'cool' because they never buy greetings cards, like they're helping the planet and being such a 'right-on' environmental activist.
Yet the same people will have 3 cars in their one family, and have several holidays abroad a year (pre-covid) and do all sorts of 'crimes' against the environment that they don't care to acknowledge. (And they seemingly don't give a shit that the people they purport to care for are upset at not getting a card.') It's plain selfish IMO.
Also, ignore the 'adults shouldn't celebrate birthdays' brigade. It's bollocks. Of course they should - if they want to! There are such weird and bizarre attitudes towards adults actually having fun on here (from some!)