@Josephine70 Sarah is right. If you are offering the home for free, it's not an Airbnb booking - if they're not collecting their fees, they have no reason to offer you any kind of coverage.
If this person is only a second-hand contact whom you don't know very well, a written rental contract and security deposit would be the normal ways to protect yourself. Even if you wish to offer the home in the spirit of charity, you are still providing long-term housing, with all the rights and obligations implied by that. There should be a clear understanding of what is "free" and what expenses the guest is expected to cover - for example, are you footing the bill for unlimited use of the utilities?