The bubble represents the mental, emotional, and physical space to which the love between Q and S exists. It’s a metaphorical form of multiple things – from their phone conversations, letters, all the way to when they’re holding hands.

…the bubble…
An indention in time-space – a microcosm where only two distinct souls exist. Their unimpeded synergy generates so much creative/attractive force, that it must be contained within its own dimension of existence. Separate, but parallel to the physical reality most currently experienced…

– QMP

The bubble takes many forms and has developed many functions, from bubble bursting, when they are returning back to reality after 100% recharge, to bubble highs and bubble hangovers, which are self explanatory.

Just as the womb serves as an incubator to newly forming infantile, so does the bubble. It serves as a space by which the the processes necessary for the two apparent souls will evolve into a more perfect and more whole being, and can be properly isolated and nurtured.

-QMP

The bubble acts as an isolated space of their love, where they can recharge and eventually go out into the world, and spread that love and energy out to others.

The bubble, as with all constructs erected of spiritual forces, being more ethereal and idealistic in being, is impervious to physical damage. Only the disconnection, and interruption of the kindred spirits’ synergetic bond can cause the bubble harm…

-QMP

The bubble is fragile and can fluctuate in strength and power depending on the situation. Since the bubble is transparent and sensitive, the building and preparation of the bubble is extensive and is in constant work-in-progress maintaining its stability.

The love that Q and S have is strong enough to handle something as fragile as a bubble – to keep it upstanding and growing for a lifetime.