How do we care hard without wearing each other out?

You already have the hard part right. You care about the work and the people in it. That was never the question. The real work is holding two things at once: staying open, and protecting the energy that lets you stay open. Most teams never say this out loud. They act like caring and limits are opposites, so people quietly pick one — and the team pays for it later, in someone's absence. This isn't burnout yet. It's the weight before burnout, and it's manageable if you name it now, together, instead of waiting until one of you can't carry it anymore.