It's always nice to get a surprise, and whether the book is a loan or a gift a very thoguhtful idea.
Bookbinder hat on:
It looks as if the leather is suffering form something usually called "red rot" which makes it fragile, the edges crumbly and powdery, sad to say there is very little that can be done to fix this, it can be stablised to consolodate , but it's can't be reversed. It's a very common problem with books from the mid-nineteenth century onwards. It's usually a result of fairly strong chemicals being used to process the leather initially, but with the mass popularisation of books and reading, and the demand that every home should have books, the economics of selling were more important than that of quality.
The book can certainly be re sewn so that it can once again be used easily, but I would suggest that a new "working cover" be used and the original be preserved.
I repaired a copy of Burns several years ago which was in a much worse state than that, and now it can be used freely without fear of dammaging it. I created a completely new cover for it, as the original was so far gone,

some more pictures of it here Robert Burns book I also made a slip case for it and covered it with "Burns" tartan.
Whatever happens the book , I hope you enjoy reading it