What to do???
First I keep emergency nail care tools will my pencils. This way I take care of any chip or tear before it gets big. It is very easy to just keep working and not fix a chipped nail, if you have to go somewhere to find these things.
I think most people push the back of a hand sewing needle with their middle finger and that can destroy that nail. Learning to sew with a thimble can be so frustrating and discouraging at first, but if you sew a lot, tough it out. It will make hand sewing so much more pleasant and faster!
I didn't know how to use a thimble until I had been working has a hand stitcher in my first professional costume shop when I was 21. After one week my right middle finger was SO sore and the nail was SO badly damaged, I got a thimble (the metal one on the left actually, a good old friend) and had a couple days of awkwardness, but then it started to just feel like a part of my hand.
So ... you, too, can learn to do this. Here is a link to a really good Youtube video showing how to use a thimble.
And when things are really bad I use this special nail polish. It helps, too. No one of these things solves the problem. But, the combination of them does.
Actually the best thing for my nails is going on a long vacation. Sewing is hard on your hands, but I love to sew and this is how I manage.