Merriam-Webster Online Defines...

... defines the word gravity as:

1 a: dignity or sobriety of bearing b: importance, significance; especially : seriousness c: a serious situation or problem2: weight3 a (1): the gravitational attraction of the mass of the earth, the moon, or a planet for bodies at or near its surface (2): a fundamental physical force that is responsible for interactions which occur because of mass between particles, between aggregations of matter (as stars and planets), and between particles (as photons) and aggregations of matter, that is 10-39 times the strength of the strong force, and that extends over infinite distances but is dominant over macroscopic distances especially between aggregations of matter —called also gravitation, gravitational force — compare electromagnetism 2a, strong force, weak force b: acceleration of gravity c: specific gravity

Fuck.

That's a lot to tackle for one girl.

And wouldn't it be egocentric for said girl to believe that she were the only one to suffer? As if she were the only moon circling his planet? Stupidly romantic. Another stubborn sucker. Another victim of the brainwash known as Disney. Everyone knows real fairy tales don't end happily ever after. The best a girl can hope for is a high tower all to herself as opposed to the harsh reality of Bluebeard's castle.

So... dignity or sobriety of bearing. She thinks she likes that. She likes it like she likes the sound of "unbearable lightness of being." She's a sucker for the pretty things no matter what lies beneath the surface. Fearless, careless, stupid or a fair share of it all.

It's still too heavy.

Which would account for the seriousness and weight part. And she wonders how long can someone last under all that weight? Years, apparently. And she tries to count them... the years... the moments... and she can't seem to remember the last time he laughed without that hollow sound... and she's sad again.

But what really floors her at those moments when the whole world has gone to bed and she's left all alone with her thoughts and wild imagination is this specific part of the definition:

a fundamental physical force that is responsible for interactions which occur because of mass between particles, between aggregations of matter (as stars and planets), and between particles (as photons) and aggregations of matter, that is 10-39 times the strength of the strong force, and that extends over infinite distances but is dominant over macroscopic distances especially between aggregations of matter —called also gravitation, gravitational force.

...and she can still hear him tell her that everything in between is not just so much unfinished business... that it's more than just a fairy tale... that their story is a rare story... he used the word clandestine... and she fell in love.