This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
It shouldn't be related to needing to make it bi-directional.
Usually the best approach is to remove the object from the collection, then update/save the parent object. The cascade option on the collection and Hibernate seeing it has been removed from the collection will tell hibernate to delete the removed object.