final Transaction tx = s.beginTransaction();

EntityA entityA1 = s.get( EntityA.class, entityA.id );
EntityB selectedEntityB = entityA1.selectedEntityB;

// clear all references between the two entities
entityA1.selectedEntityB = null;
entityA1.listOfEntityB.clear();

selectedEntityB.entityA = null;

// then remove both entities
s.remove(entityA1);
s.remove(selectedEntityB);

tx.commit();

EntityA entityA1 = session.merge( entityA );
EntityB selectedEntityB = entityA1.selectedEntityB;

// clear all references between the two entities
entityA1.selectedEntityB = null;
entityA1.listOfEntityB.clear();
selectedEntityB.entityA = null;

// then remove both entities
session.remove( entityA1 );
session.remove( selectedEntityB );