mummmalugs you;'ve painted a more full picture now and I feel that it is a bit shakey to me. And you have not make it more shakey!
"He does tend to see our problems as being my fault and not his, so thinks it's me that needs the counselling." OK so what problems does he see? (I am quite sure they are not your fault, that kind of blanket 'it's all her and not me' seems to come from a certain place of 'assurance', which I feel is unlikely to be true. I would imagine if you have problems there is some blame to both sides or maybe it is all him, I can't see how it can all be you when you are willing to get counseling and work on things. The fact he is unwilling to work at it suggests he is the cause of some of the things (to me).
You've got three children and one is very young, so you both have a lot on your plate, but I am guessing you are on maternity leave or are the main carer for three kids, (that's pretty standard, is that so for you?).
"But my DH does have some anger there..." is this anger directed at you, the kids, his own family, some combination of these factors?
"...perhaps from his own family life as a child." Did he have what might be called a 'deprived childhood'? If so it does seem very relevant that he gets counselling about this so he can ensure this doesn't continue to hurt him and damage and jeopardize his life now, IMHO.
"It's tricky." Can you explain what this means? Tricky for him, tricky for you, tricky for you to help him, tricky for him to trust you, tricky like you are walking on egg shells the whole time or am I imagining that because in so many relationships where the man has issues, these issues affect the wife and the family? (I am sure it would be the same if the roles were reversed but I don't read about many families where this is the case.)
"His unwillingness to face that may be part of a lot of these problems."
It seems clear it is.
So there is a big discrepancy in your upbringing? You have a family with money etc (support, love etc) and he had a much poorer upbringing or one where there was a lot less love or a lot less support?
I think you can either hide from this, as he appears to be doing, and carry on, or seek some counselling to reconcile these differences and work things out together.
Certainly for me it felt normal/natural to share the inheritance I got (which was relatively small, I can't even remember now but say between 6 and 8 K) with my dh. But if my dh had been musing about our not being together I would have felt differently.
From your OP it is clear that your dh has already benefited from your parents, as have you, ".... including the money my parents have gave us to help buy our first apartment."
Has receiving this money made him feel emasculated? I think this really is his problem to work through, your parents helped you out, as mine did with money for fertility treatment. (Ironically the money my mum gave us was probably more than twice what we eventually inherited because this was years ago before she got ill).
But it also seems clear any issues were there before the day you posted and started this thread, the day mentioned about the inheritance.
Because you said "We've had a few rough patches lately. During a couple of arguments he's suggested he could conceivably leave me/separate. Although we've always patched things up. It totally rocked my confidence at the time. I have never made this threat to our marriage."
So you are not the one who has caused this current 'shakiness'!