From Path of the Vampire Wiki
The eternal bond refers to a mystical connection between two characters. On grid, this grants a few small, invisible stat bonuses when the two characters are in the same square. The bond is formed through a ritual.
You can now unbind from your companions. The fee is 10 karma (to dissuade people from doing it), and this can be purchased via the karma shop. This will remove your companion and leave you free to re-bind once more. Companions of characters who delete themselves will also now become bound to nobody, and free to rebind once more.
There is no IC reason for unbinding, other than permanent death. That isn't to say that unbinding is crossing, it's just to say that there's no ritual or spell which does it IC. This change was made to be fairer to characters whose companions have deleted themselves, or those who have OOC issues with their IC companion.