why are you mothering him? if he can't be arsed making his own lunch - then let him go without. i doubt very much he'l starve - he'll either start making them himself or buy lunch from somewhere.
the things he does with your dc - well that's what fathers are meant to do so he doesn't deserve special recognition for it - do you get special recognition for doing your job as a mum?
i work in car finance and your dp is taking the piss big style.
First of all, unless you've seen the documents you won't know if he's applied in your name.
If the car is in his name he can drive away with it anytime and there's bugger all you can do about it.
If the finance is in his name then although the debt is technically his YOU will be contributing towards it. Hence why he just CAN'T make this decision on his own unless he pays for the car and finance out of his 'spending' money. If it comes out of family then it HAS to be a joint decision. Plus the relative is from your side of the family!
If you intend on letting him use someone elses money - and it is a loan - then you need it down in writing and signed by him and witnessed. If he leaves you there is nothing to say he 'owes' your relative anything and he could claim the money was a gift.
He can also easily sell the car anytime. He could make a big profit on it - now or in the future - and neither you nor your relative may see any of it because he'll make sure of that.
if you're going to do this then you need to be business like about it and make sure you and your relative are legally protected.
however........after so many years if he doesn't have any respect for you and treats you like this - why do you want to stay with him?