Does 2 instance of booming blade stack?


I’m creating a NPC for a campaign that is a sorcerer using a long sword and the booming blade spell.

Booming Blade

Level: Cantrip

Casting time: 1

Action Range: 5 feet

Components: V, M(a weapon)

Duration: 1 round

As part of the action used to cast this spell, you must make a melee attack with a weapon against one creature within the spell’s range, otherwise the spell fails. On a hit, the target suffers the attack’s normal effects, and it becomes sheathed in booming energy until the start of your next turn. If the target willingly moves before then, it immediately takes 1d8 thunder damage, and the spell ends. This spell’s damage increases when you reach higher levels.

At higher level At 5th level, the melee attack deals an extra 1d8 thunder damage to the target, and the damage the target takes for moving increases to 2d8. Both damage rolls increase by 1d8 at 11th level and 17th level.

With the Metamagic option Quickened Spell, this NPC can cast booming blade twice per turn. So here is my question: Do 2 instances of booming blade stack?

By instances of booming blade, I meant the part that reads:

If the target willingly moves before then, it immediately takes 1d8 thunder damage, and the spell ends.