This is a good site that offers helpful advice to people who feel they may need to give up their dog. It looks at some of the common reasons and offers some solutions and ways of approaching what might, right now, seem an insurmountable problem.
If you are considering giving up your cavalier, be sure to contact your local or regional cavalier rescue group first. Links to organisations internationally are listed at the top of the Breed Rescue forum. Rescues will make absolutely sure your dog goes to the best possible home. Cavaliers handed in to pounds or shelters can go to anyone and homes generally are not homechecked, or may be put to sleep.