An irrational fear is just that ..... irrational. You can't explain it or understand it.
But this isn't that, an accident that left you stranded ?
A partner who grabbed the wheel ?
These are not irrational, or stupid, this is a fear based on your experiences, a very RATIONAL reaction.
All the advice given is great, get your own car, take special lessons, (they do ones for motorways,snow, all sorts now) therapy, but most of all, stop blaming yourself.
Would you blame someone scared of dogs after being attacked ? Or scared of water after nearly drowning ? Of course not, you would offer them sympathy, and help them get over their fears, not call their fears stupid.
Does he know about the wheel thing ? Have you really told him how it made you feel, the pit in your stomach ? The band around your chest that stops you taking a breath ?
If not, do.