"Ripping a card up from children seems so personal, so... Intimately hateful."
Yes, he did it to hurt you, OP. And he either didn't care that the kids could have found it, or he would have liked them to find it so that he could then blame you for "making me hurt the kids".
This is fucked up thinking, OP. And that blame-wife-for-my-own-actions thinking is a total HALLMARK of an ABUSIVE man.
Having a terrible childhood does not excuse abusive behaviour. Nothing does.
You mentioned that the kids adore him. You may not realise this, but children often become anxiously pleasing and apparently 'adoring' with a parent who is volatile and makes them feel unsafe. They are dependents, they are likely to feel that they have to keep Dad calm and happy so that he doesn't get mad.
This is an EXTREMELY unhealthy environment for children to grow up in. If you split, the children will be with you - the sane, calm, devoted, steady parent - at least 50% of the time (probably more). That's better than living 100% of the time walking on eggshells around this mean moody man.
You also said the kids would be 'devastated' by the split. You also said "I’ve found all the times he has not been with us recently to be a massive relief. No moodiness, lack of presence."
I bet you the kids were also relieved deep down, OP. Staying with this man risks them lifelong torment and therapy bills, whereas leaving calmly and setting up 2 houses and coparenting will not.