Can my players abuse this homebrew Blade of the Thirst magic item?

I am designing a homebrew magic item. I think I have it balanced but need to know if there are any loopholes I have not seen.

Blade of the thirst, magical longsword, requires attunement, versatile, finesse.

The weapon of an ancient vampire lord, the blade of the thirst is imbued with the vampire’s lust for blood.

A black longsword with a guard made up of 3 carved black roses; the guard is gripped thorned vines that extend from the roses and bind to the wielder’s wrist.

Blade of the thirst confers proficiency for itself onto the wielder.
At the start of the wielder’s turn the blade of thirst drains blood from its wielder, causing 1/2/3 damage to the wielder (player’s choice); the sword counts as a +x weapon until the end of the turn, where x is the damage caused to the wielder.

  1. Is this magic item balanced?
  2. Is there an obvious way to abuse it?