Do I have to give up my home in Germany when I move to Bulgaria?

For tax purposes yes, if German tax liability is to end. Under section 8 of the German Fiscal Code a person has a residence where they occupy a dwelling in circumstances indicating that they will keep and use it. A home kept ready for occupation and available to you at any time establishes residence even if rarely used, and unlimited tax liability under section 1(1) sentence 1 of the Income Tax Act therefore continues. Long-term letting to third parties changes the assessment; occasional use by friends generally does not. Deregistering at the residents' registration office is not enough on its own; the actual circumstances decide. General information, not tax advice.