Ilovekimpossiblealot would approves.  
But, I am neutral.

Would never happen

Fluttershy wouldn’t be crying… She’d be shipping them together and helping Discord get to Celestia. Celestia is superior to Fluttershy. Little girls can’t always date their old man crushes.

Yes cry! Cry! Cry Tears of….Happiness! OH COME ON!

@Alara Rogers  
True, Twilight would fit in that place in the first place. Although i would also see Fluttershy act at least a little concerned. As you said, she would grieve her lack of confidence + that she lost her close friends who will most likely won’t find any time to spend time with her anymore.

This kind of bugs me… it doesn’t quite feel in character.
 
Fluttershy perceives Celestia as being far, far above herself. And she doesn’t have the highest of self esteem to begin with. To grieve like this because the one you love loves someone else, you’d kind of had to have thought you had a chance in the first place. And unless Discord has been leading her on, I would think that the fact that he hooked up with Celestia would be a retroactive statement to Fluttershy that she didn’t have a chance.
 
I could see her reacting like this to Twicord or Discopie, because Twilight and Pinkie are her equals, but if Discord hooks up with Princess Celestia I’d think this would tell Fluttershy (Fluttershy in particular, who has low self esteem) that Discord was never in her league in the first place.
 
This would actually be more interesting the other way around. Celestia deliberately asked Fluttershy to reform Discord and more or less handed him over to her, so if Celestia was weeping because Discord had hooked up with Fluttershy, it would imply less jealous heartbreak and more sorrow for what was and what could never be – like, she gave Discord to Fluttershy knowing this might happen, hoping it would happen, but when it does it just reinforces her own feelings of failure that she wasn’t able to save him herself.
 
I suppose it’s always possible that yes, Discord has been leading Fluttershy on. Given the extreme unlikelihood of Chaos respecting the concept of monogamy, he might even be cheating on Fluttershy with Celestia here (though the title “I’m happy if you are” suggests that’s not what’s going on.)

I’m really looking forward to that Smooze episode…

Don’t be sad Flutters! Just ask Dash to rainnuke Canterlort, and he will be yours! Forever…