Really? Camp is a "need"? WOW, right back at 'ya. And yes, a child who is in serious turmoil (pain/anger/sadness/trauma of any kind) should absolutely be given first priority, at that moment. It's not as though the younger one will NEVER be able to ride in a car. It's a temporary situation, which is why I said I'm sure the older one will manage just fine being at home for a few months. Daily social outings are NOT A NEED. There are plenty of things that could be done at home or withing walking/bus distance (whichever is available, depending on your location) to keep an older child happy and fulfilled without causing trauma to the younger child.
eta: I'm not saying that the OP should NEVER drive. Obviously, there are times when you just have to. But the suggestion that "it's not fair" to keep the older child at home every day temporarily doesn't make any sense to me.
Umm I have a child for whom getting out every day IS a need. And we live in an area where that need simply *can't* be fulfilled by walking or buses or whatever. I certainly wouldn't argue that the OP can evaluate whether camp is a want or a need for her son, but to make a sweeping generalization that "Daily social outings are NOT A NEED," is not accurate, nor is the assumption that everyone lives in an area where cars are optional.
Ironically, my needs-to-get-out DS is the same one who HATED the car for his first year and still struggles with it. Every day I had to weigh how badly he needed to get out (and myself, as well, I get severely depressed when I don't get out often enough) with his hatred of the car. Parenting involves making some really tough decisions, there is no need to place extra guilt and burden on a struggling mom because she is desperately trying to balance out the needs of everyone in the family!!! It's obvious in her posts that the OP already feels a lot of guilt, she doesn't need anyone else to add to it!
OP, if you are still around, I was wondering if you ever got to try driving with him in the convertible seat? It seems to have helped enough people that it may be worth a try if you haven't yet...