You may have heard folks talking about buying locally and environmentally friendly cultivated sage, especially by Indigenous folks. We certainly encourage this especially because most commercial white sage comes from California and with annual wildfires and drought this is not a sustainable practice.
If, however, your friend has sourced his sage himself and is doing so in a respectful manner there’s no need to waste it now that it has given its life.
In terms of using white sage to clean yourself and the spaces you occupy, make sure your sage itself is pure.
In the future, see if there are ways to support local Indigenous farmers and artists.
Hope this helps.