I think it's best if a show does diverge from the books it's based on once it establishes its own identity. For one thing, you never know which actors will break out from the pack or turn out to have chemistry. If the heroine's love interest in the book turns out to be played by an actor she has no chemistry with at all, while the minor supporting character turns out to have great chemistry with her and steals every scene he's in, it would be wrong not
to have the heroine leave the book love interest and hook up with the supporting character. The show has to be its own entity and do what best serves it as a show.