I think with issues around loneliness and rising statistics of people who feel they have no friends makes your kind of situation more rare. I think the way social structures have gone, it's rarer for people to have and maintain long-term social bonds that make these lovely stories of retiring together.
There have been times I've liked my friends more than my spouse, but I've always come back to him and have since I was 16. I immigrated at 17 so don't have anyone in my daily life that's known me longer than him.
Also, yes, a bit less than half of all marriages fail, but research into friendships has given some evidence that at the start of a 7 year period, half the people we'd view as our closest friends will no longer be in our lives for various reasons by the end. All relationships can end, even some of our longest and once strongest. They all need to be nurtured.
In an emergency situation, everyone near me knows we're all fucked. Other than maybe my youngest child, I can't drag or carry anyone. An adreneline rush is more likely going to cause me to fall over from messing with my circulation than give me super strength. I'm best suited to calling a professional.
I completely agree with your argument OP that we should put everyone on one other person's shoulders. I've far more often heard it for people arguing in favour of polyamory, but I agree it applies equally if not better in caring for our platonic friendships as well rather than tyeing all that to our romantic/sexual relationships.
However, I also agree with the previous poster that part of it might be that there is less negativity or pressure with someone we're close to and don't live with, that's why he gets 'nice guy'.
I'm in the odd situation that my lodger is my spouse's best friend and at times has been mine, we all live together, and we go through periods where we're driving each other crazy over things like lodger-friend always leaving the salt shaker and other things out on the kitchen counter and why the fuck did he say doesn't know why we're down on plates when we can see he has a stack in his room (when lodger-friend's depression is really bad, it's like having another teenager in terms of mess, I think he just gets numbed to it so didn't see it there). We get through it, but having to deal with each other's shit all the time without much break I think takes the shine off.