I don't understand, perhaps it's the way you worded it, but you seem to be paying all the outgoings from your salary, what exactly is your DH paying for?
You should go to moneysavingexpert.com and download their free excel spreadsheet which has a brilliant ready made budget planner and fill it all out.
It has included most things in it, especially smaller outgoings that you may overlook. Fill it out and then you can both see how much you spend and you can tweek it for different scenarios. It will show monthly & yearly expenditure totals and can be a real eye opener.
Once you've done this, you can then discuss how to arrange the division of expenditure. Personally I would look at the real cost of running both cars (insurance, petrol, servicing, MOT, breakdown cover, depreciation) over the year and break that down monthly, tthis will give you both a realistic budget for car costs, hopefully without an unpleasant surprise.
Your husband or you, may not realise how much outgoings you cover, little things do mount up. It is also a good way of reining in unnecessary expenditure.