OP I think you've had a hard time from some posters on this thread.
Yes, it's possible that your DH is just a decent person taking out his work-related stress on you. However ime mature adults who feel under pressure at work will discuss it rationally with their spouse - they don't insist on taking on additional debt by buying holiday homes.
The other possibility is that the "sole earner stress" line is a red herring, and he is actually a selfish person who is willing to use unpleasant controlling and manipulative behaviour to prevent you making too many demands on his nicely arranged life.
Look at what you have written:
DH brings up the fact that I gave up work and that he is the sole earner...it is usually fairly irrelevant to the argument we are having...he always brings it up as a way to score points...I can’t argue with that because it’s true
This is a classic diversionary tactic - he attacks you to divert attention from his own behaviour. I would lay money that he brings up this "issue" in disagreements where you are asking him to do something he doesn't want to do, or where he wants to do something you'd prefer he didn't do. He brings up the fact that you don't work, you stop talking about whatever it was you were discussing and instead start defending yourself against what you see as an unfair charge.
He keeps returning to the same issue time and time again because it works - you're not on MN posting about whatever it was you had your last disagreement about, are you? You're posting about whether you deserve your DH's censure. Bringing up this issue neatly switches the focus from his behaviour onto yours. It puts you on the back foot, on the defensive, has you devoting time and thought to whether you've done something wrong, how you can convince him that he's not being fair, rather than what you were originally discussing. As previous posters have suggested, if you were working, he would find something else to use as a grievance.
I am very grateful for all his hard work, and I don't give him a hard time about his working hours, or the hours that he spends on hobbies.
I bet you don't give him a hard time - you've learned that if you do, he will go on at you about not working!
I gave up work 7 years ago, and we agreed it at the time. However, he now remembers it as my unilateral decision
If it was genuinely a mutual decision, then this is gaslighting - trying to make you doubt your recollection of events. Again, as classic manipulative technique to put you on the defensive.
He wanted a holiday home which adds approx 150k of debt plus various additional bills council tax etc. This is a big drain, I think it's bonkers, but the argument from him went, "'I work so hard and this is what I want"
What about what you want? Why does he get to make major financial decisions without consulting you? Because he earns the money? The money he earns is family money. The work you do to keep your domestic life running allows him to work the hours he does to earn this money. To dismiss you right to input on financial decisions is a marker for how much he respects you.
He is quite an anxious type, likes everything under control
Everything including you.
I listen to him talking about work and try to help him suggesting he delegates more, sets boundaries around his working hours, stuff like that. But this is unsupportive apparently, and I don't understand.
To a self-centred, controlling personality, a difference of opinion may be perceived as a hostile act (lesser mortals are not supposed to have their opinions, just agree with the ones presented to them). Does he also accuse you of starting arguments if you express a difference of opinion or politely disagree with him?
I merely sometimes express concern about his hours of work, and wish he could manage his job without always working the 12 hour days every day, plus looking at work on his laptop evenings and weekends...I can't help wishing he was a bit more available to the family sometimes
These don't sound to me like unreasonable demands from a nagging wife. It sounds as if you just want a partner who participates willingly in family life.
Some posters have suggested that you and your DH have a communication issue. I suspect you may well have expressed your wishes perfectly reasonably and clearly in the past, but your DH is not listening because a) he doesn't respect you enough to take you seriously and b) listening to you might mean having to adjust his behaviour and he has no intention of doing that.
There is nothing to be lost from sitting down with him and trying once again to spell out your concerns. If he tries to divert the conversation by bringing up your not working, just say "that's not what we're discussing at the moment, we're discussing xyz so let's stick with that".
You manage a household and 3 DCs, work part-time and are completing a doctorate. That's an impressive workload by anyone's standards and you deserve more respect than your DH seems willing to give you.