Looks like Maidenhair. These must not be allowed to dry out, if that's any help?

Is it in bright light/direct sun? it needs some shade. Which fern is it? if it is a native fern it needs to be outside not indoors.

I was going to suggest , might it be positioned in full sun ? Indirect light ,and lots of misting,as they like Humidity. Also standing it on pebbles ,or gravel,inside your outer pot might help too. As SBG suggests, it could need to be outside .If you google Maidenhair Fern,you will find lots of advice which you may find helpful..good luck,Charnwood. :o)

But don't give up on it, even if these leaves die back it should shoot out again from the root. Too much sun or heat I would think.

In the past I did have one that looked very similar which lived happily in the house for a long time, sprayed with water from time to time. Don't know if it was a different variety from the garden one.