My favorite thing about The Mortal Instruments? There's vows for the best friends in it. And i think that's beautiful.
"Entreat me not to leave thee,
Or return from following after thee—
For whither thou goest, I will go,
And where thou lodgest, I will lodge.
Thy people shall be my people, and thy God my God.
Where thou diest, will I die, and there will I be buried.
The Angel do so to me, and more also,
If aught but death part thee and me."
Like come on that level of loyalty