I don’t think Hook will hurt Belle. His plan at the moment is to kill Rumple and he has had that goal since Rumple killed Milah. If Hook were to kill Belle, it would cause Rumple pain but Hook would then be putting Rumple out of his misery by killing him. Hook will probably get close to Belle and then make it clear to Rumple how easily he could hurt Belle, without actually laying a finger on her. Rumple will then probably get overprotective of Belle which could then drive her away.
However, if Rumple is honest with Belle about why Hook is such a danger to her then she can at least take steps to protect herself should Hook come calling. Hook’s become a regular so he is going to be around Storybrooke for quite a while.
All magic comes with a price!
Keeper of Felix