Is there a library where I can rent english books/novels?

you need to go to the muncipality

All libraries in Mauritius stock a selection of English/French as well as Hindi/Urdu/Chinese books. Some municipal libraries may have more of one language than another. So I think it's a good idea to sign up to your municipal library so you can borrow books.

The National Library of Mauritius has a search facility for their online catalogue where you can check books you're interested.

Many bookshops also sell second hand books, just ask them. There's one at La Rue Desforges in Port-Louis which I know for sure but can't remember the name.